diff --git a/README.md b/README.md
index 0e109c0..90cb622 100644
--- a/README.md
+++ b/README.md
@@ -35,7 +35,7 @@ dotnet test RioJoy.sln
 
 ## Status
 
-Phases 2–3 (serial + RIO protocol core, input mapping + output routing) are
-code-complete and unit-tested; the virtual-HID feeder and hardware verification
-are pending on the Phase 1 driver. See [`docs/PLAN.md`](docs/PLAN.md) for the full
-roadmap.
+Phases 2–4 (serial + RIO protocol core, input mapping + output routing, axis
+calibration + plasma display) are code-complete and unit-tested (105 tests); the
+virtual-HID feeder and hardware verification are pending on the Phase 1 driver.
+See [`docs/PLAN.md`](docs/PLAN.md) for the full roadmap.
diff --git a/docs/PLAN.md b/docs/PLAN.md
index c321df5..1f2de5f 100644
--- a/docs/PLAN.md
+++ b/docs/PLAN.md
@@ -149,9 +149,20 @@ Implemented in `src/RioJoy.Core/Mapping` + `Output`, covered by the
   driver exists. The legacy default map / `RIO.ini` becomes an importable profile
   (Phase 5/7).
 
-### Phase 4 — Axis calibration + plasma display
-- Port `UpdateJoystick/Throttle/Padal` math (deadzones, ratchet, rudder).
-- Port the `CPlasma` ESC command set on the secondary COM port.
+### Phase 4 — Axis calibration + plasma display — code-complete ✅
+Implemented in `src/RioJoy.Core/Calibration` + `Plasma` (105 xUnit tests total):
+- `AxisCalibrator` ports `UpdateThrottle`/`UpdatePadal`/`UpdateJoystick`: throttle
+  deadzone + ratchet field, pedal deadzones, X/Y auto-ranging from observed
+  min/max, rudder mixing (`enableZR`), and all per-axis invert flags. Stateful
+  (start positions, last outputs) like the legacy globals, with the RIOcmd axis
+  resets. Outputs clamp to the documented `0..32766` range.
+- `IJoystickSink` gains `SetAxis(JoyAxis, value)` so calibrated axes reach the HID
+  feeder; `AxisOutputs` carries the six values.
+- `PlasmaCommands` ports the `CPlasma` ESC command set (clear/cursor/font/attr/box
+  draw+fill/text) + `GetFontSize` + the `PlasmaPosText` auto-fit/centering;
+  `PlasmaDisplay` writes them over the secondary COM transport.
+- ⏳ **Remaining:** hardware verification of axis feel + plasma output; the
+  game-specific `PlasmaScoreDraw` layout is profile content (Phase 5/7).
 
 ### Phase 5 — Tray app + profiles
 - NotifyIcon + menu mirroring the legacy console menu (reset/recalibrate axes,
diff --git a/src/RioJoy.Core/Calibration/AxisCalibrationConfig.cs b/src/RioJoy.Core/Calibration/AxisCalibrationConfig.cs
new file mode 100644
index 0000000..1bbfbbc
--- /dev/null
+++ b/src/RioJoy.Core/Calibration/AxisCalibrationConfig.cs
@@ -0,0 +1,21 @@
+namespace RioJoy.Core.Calibration;
+
+/// <summary>
+/// Per-profile axis calibration options. Defaults mirror the legacy
+/// <c>JoyStick</c> ini section (riovjoy2.cpp#L345): all inverts off,
+/// <see cref="EnableZR"/> on. When <see cref="EnableZR"/> is set, the pedals are
+/// mixed into a single rudder axis (Rz) and Rx/Ry are held centered; when clear,
+/// the pedals drive Rx/Ry directly and Rz is held centered.
+/// </summary>
+public sealed record AxisCalibrationConfig
+{
+    public bool InvertX { get; init; }
+    public bool InvertY { get; init; }
+    public bool InvertZ { get; init; }
+    public bool InvertXR { get; init; }
+    public bool InvertYR { get; init; }
+    public bool InvertZR { get; init; }
+
+    /// <summary>Mix the two pedals into a rudder axis (Rz). Legacy default: on.</summary>
+    public bool EnableZR { get; init; } = true;
+}
diff --git a/src/RioJoy.Core/Calibration/AxisCalibrator.cs b/src/RioJoy.Core/Calibration/AxisCalibrator.cs
new file mode 100644
index 0000000..14387fb
--- /dev/null
+++ b/src/RioJoy.Core/Calibration/AxisCalibrator.cs
@@ -0,0 +1,271 @@
+using RioJoy.Core.Protocol;
+
+namespace RioJoy.Core.Calibration;
+
+/// <summary>
+/// Converts raw RIO analog samples into calibrated virtual-joystick axis values.
+/// Stateful port of <c>UpdateThrottle</c>/<c>UpdatePadal</c>/<c>UpdateJoystick</c>
+/// (riovjoy2.cpp#L1504+); see docs/PROTOCOL.md §4. State (auto-ranging start
+/// positions, observed min/max for X/Y, last outputs, throttle ratchet) carries
+/// across <see cref="Update"/> calls exactly as the legacy globals did.
+///
+/// <para>Final outputs are clamped to <c>0..<see cref="AxisOutputs.Max"/></c> — the
+/// documented axis range — which also guards a legacy quirk where a value pinned
+/// at its observed extreme could compound across polls (see ⚠️ below).</para>
+/// </summary>
+public sealed class AxisCalibrator
+{
+    private const int RangeThrottle = 800;
+    private const int DeadzoneThrottle = 50;
+    private const int RangePadal = 500;
+    private const int DeadzonePadal = 10;
+    private const int DeadzoneJoystick = 5;
+
+    private readonly AxisCalibrationConfig _config;
+
+    // Auto-ranging start positions.
+    private int _throttleStart = int.MinValue;
+    private int _leftPedalStart = int.MaxValue;
+    private int _rightPedalStart = int.MaxValue;
+
+    // Last computed (pre-clamp) outputs — persist across calls like the legacy globals.
+    private int _throttleLast = AxisOutputs.Center;
+    private int _leftPedalLast = AxisOutputs.Center;
+    private int _rightPedalLast = AxisOutputs.Center;
+    private int _joystickXLast = AxisOutputs.Center;
+    private int _joystickYLast = AxisOutputs.Center;
+
+    // Throttle ratchet direction. Initialized -1; the legacy never sets it
+    // positive, so the "back" branches are effectively dead but ported faithfully.
+    private int _throttleResult = -1;
+
+    // Observed min/max for the joystick axes (auto-ranging rate).
+    private int _minX, _maxX, _minY, _maxY;
+
+    public AxisCalibrator(AxisCalibrationConfig? config = null)
+    {
+        _config = config ?? new AxisCalibrationConfig();
+    }
+
+    /// <summary>
+    /// Calibrate one raw analog sample and return the six axis values. Updates the
+    /// observed X/Y min/max first (as the legacy <c>AnalogEvent</c> did), then runs
+    /// the per-axis math.
+    /// </summary>
+    public AxisOutputs Update(AnalogReport raw)
+    {
+        _maxX = Math.Max(raw.JoystickX, _maxX);
+        _minX = Math.Min(raw.JoystickX, _minX);
+        _maxY = Math.Max(raw.JoystickY, _maxY);
+        _minY = Math.Min(raw.JoystickY, _minY);
+
+        int z = Throttle(raw.Throttle);
+        (int rx, int ry, int rz) = Pedals(raw.LeftPedal, raw.RightPedal);
+        int x = JoystickX(raw.JoystickX);
+        int y = JoystickY(raw.JoystickY);
+
+        return new AxisOutputs(
+            Clamp(x), Clamp(y), Clamp(z), Clamp(rx), Clamp(ry), Clamp(rz));
+    }
+
+    private static int Clamp(int v) => Math.Clamp(v, 0, AxisOutputs.Max);
+
+    private int Throttle(int throttle)
+    {
+        if (throttle < -RangeThrottle || throttle > RangeThrottle)
+        {
+            if (throttle < RangeThrottle)
+                _throttleLast = _throttleResult > 0 ? 1000 : -1000;
+            else
+                _throttleLast = 0;
+        }
+        else
+        {
+            if (_throttleStart < throttle)
+                _throttleStart = throttle;
+
+            int lT = _throttleStart - throttle;
+            if (lT > 800)
+                lT = 800;
+
+            if (lT != 0)
+            {
+                lT = lT * 1000 / 800;
+                if (lT is > -DeadzoneThrottle and < DeadzoneThrottle)
+                    _throttleLast = 0;
+                else if (_throttleResult > 0) // back
+                    _throttleLast = 900 + (lT * _throttleResult / 10);
+                else // front
+                    _throttleLast = lT * _throttleResult;
+            }
+            // lT == 0 leaves _throttleLast unchanged (legacy behavior).
+        }
+
+        _throttleLast = Math.Abs(_throttleLast * 32);
+        return _config.InvertZ ? AxisOutputs.Max - _throttleLast : _throttleLast;
+    }
+
+    private (int rx, int ry, int rz) Pedals(int leftPedal, int rightPedal)
+    {
+        // LEFT pedal
+        if (leftPedal < -RangePadal || leftPedal > RangePadal)
+        {
+            _leftPedalLast = leftPedal > RangePadal ? -1000 : 0;
+        }
+        else
+        {
+            if (_leftPedalStart > leftPedal)
+                _leftPedalStart = leftPedal;
+
+            int lP = _leftPedalStart - leftPedal;
+            if (lP != 0)
+                lP = lP * 1000 / RangePadal;
+            if (Math.Abs(lP) < DeadzonePadal)
+                lP = 0;
+            _leftPedalLast = lP;
+        }
+        _leftPedalLast = Math.Abs(_leftPedalLast * 32);
+        if (_config.InvertXR)
+            _leftPedalLast = AxisOutputs.Max - _leftPedalLast;
+
+        // RIGHT pedal
+        if (rightPedal < -RangePadal || rightPedal > RangePadal)
+        {
+            _rightPedalLast = rightPedal > RangePadal ? 1000 : 0;
+        }
+        else
+        {
+            if (_rightPedalStart > rightPedal)
+                _rightPedalStart = rightPedal;
+
+            int lP = _rightPedalStart - rightPedal;
+            if (lP != 0)
+                lP = lP * 1000 / RangePadal;
+            if (Math.Abs(lP) < DeadzonePadal)
+                lP = 0;
+            _rightPedalLast = -lP;
+        }
+        _rightPedalLast = Math.Abs(_rightPedalLast * 32);
+        if (_config.InvertYR)
+            _rightPedalLast = AxisOutputs.Max - _rightPedalLast;
+
+        int rudder = AxisOutputs.Center - (_leftPedalLast / 2) + (_rightPedalLast / 2);
+        if (_config.InvertZR)
+            rudder = AxisOutputs.Max - rudder;
+
+        // EnableZR mixes the pedals into the rudder (Rz) and centers Rx/Ry;
+        // otherwise the pedals drive Rx/Ry directly and Rz is centered.
+        int rx = _config.EnableZR ? AxisOutputs.Center : _leftPedalLast;
+        int ry = _config.EnableZR ? AxisOutputs.Center : _rightPedalLast;
+        int rz = _config.EnableZR ? rudder : AxisOutputs.Center;
+        return (rx, ry, rz);
+    }
+
+    private int JoystickX(int joystickX)
+    {
+        int startingLeftRate = Math.Min(_minX, -80);
+        int startingRightRate = Math.Max(_maxX, 80);
+        int sLeftRate = AxisOutputs.Center / (Math.Abs(startingLeftRate) - DeadzoneJoystick);
+        int sRightRate = AxisOutputs.Center / (startingRightRate - DeadzoneJoystick);
+
+        int lJx = joystickX;
+        if (lJx < 0) // LEFT
+        {
+            lJx += DeadzoneJoystick;
+            _joystickXLast = lJx < 0 ? AxisOutputs.Center - (lJx * sLeftRate) : AxisOutputs.Center;
+        }
+        else if (lJx > 0) // RIGHT
+        {
+            lJx -= DeadzoneJoystick;
+            // 16838 (not 16383) and a +2 nudge are deliberate legacy anti-snap tweaks.
+            _joystickXLast = lJx > 0 ? 16838 - ((lJx + 2) * sRightRate) : AxisOutputs.Center;
+        }
+        // lJx == 0 leaves _joystickXLast unchanged (legacy behavior).
+
+        return _config.InvertX ? AxisOutputs.Max - _joystickXLast : _joystickXLast;
+    }
+
+    private int JoystickY(int joystickY)
+    {
+        int startingUpRate = Math.Min(_minY, -80);
+        int startingDownRate = Math.Max(_maxY, 80);
+        int sUpRate = AxisOutputs.Center / (Math.Abs(startingUpRate) - DeadzoneJoystick);
+        int sDownRate = AxisOutputs.Center / (startingDownRate - DeadzoneJoystick);
+
+        int lJy = joystickY;
+        if (lJy < 0) // UP
+        {
+            lJy += DeadzoneJoystick;
+            _joystickYLast = lJy < 0 ? AxisOutputs.Center - (lJy * sUpRate) : AxisOutputs.Center;
+        }
+        else if (lJy > 0) // DOWN
+        {
+            lJy -= DeadzoneJoystick;
+            _joystickYLast = lJy > 0 ? AxisOutputs.Center - (lJy * sDownRate) : AxisOutputs.Center;
+        }
+        // lJy == 0 leaves _joystickYLast unchanged (legacy behavior).
+
+        return _config.InvertY ? AxisOutputs.Max - _joystickYLast : _joystickYLast;
+    }
+
+    // --- Resets (port of the RIOcmd axis-reset cases, riovjoy2.cpp#L1852) -------
+
+    /// <summary>Dispatch a calibration reset for a RIO-command reset code.</summary>
+    public void Reset(Mapping.RioCommandCode command)
+    {
+        switch (command)
+        {
+            case Mapping.RioCommandCode.ResetAllAxes: ResetAll(); break;
+            case Mapping.RioCommandCode.ResetThrottle: ResetThrottle(); break;
+            case Mapping.RioCommandCode.ResetLeftPedal: ResetLeftPedal(); break;
+            case Mapping.RioCommandCode.ResetRightPedal: ResetRightPedal(); break;
+            case Mapping.RioCommandCode.ResetVerticalJoystick: ResetVerticalJoystick(); break;
+            case Mapping.RioCommandCode.ResetHorizontalJoystick: ResetHorizontalJoystick(); break;
+        }
+    }
+
+    public void ResetAll()
+    {
+        _throttleResult = -1;
+        _throttleStart = int.MinValue;
+        _leftPedalStart = int.MaxValue;
+        _rightPedalStart = int.MaxValue;
+        _joystickXLast = AxisOutputs.Center;
+        _joystickYLast = AxisOutputs.Center;
+        _throttleLast = 0;
+        _leftPedalLast = 0;
+        _rightPedalLast = 0;
+        _minX = _maxX = _minY = _maxY = 0;
+    }
+
+    public void ResetThrottle()
+    {
+        _throttleResult = -1;
+        _throttleStart = int.MinValue;
+        _throttleLast = 0;
+    }
+
+    public void ResetLeftPedal()
+    {
+        _leftPedalStart = int.MaxValue;
+        _leftPedalLast = 0;
+    }
+
+    public void ResetRightPedal()
+    {
+        _rightPedalStart = int.MaxValue;
+        _rightPedalLast = 0;
+    }
+
+    public void ResetVerticalJoystick()
+    {
+        _joystickYLast = AxisOutputs.Center;
+        _maxY = _minY = 0;
+    }
+
+    public void ResetHorizontalJoystick()
+    {
+        _joystickXLast = AxisOutputs.Center;
+        _maxX = _minX = 0;
+    }
+}
diff --git a/src/RioJoy.Core/Calibration/AxisOutputs.cs b/src/RioJoy.Core/Calibration/AxisOutputs.cs
new file mode 100644
index 0000000..fca59e2
--- /dev/null
+++ b/src/RioJoy.Core/Calibration/AxisOutputs.cs
@@ -0,0 +1,45 @@
+namespace RioJoy.Core.Calibration;
+
+/// <summary>
+/// The six calibrated virtual-joystick axis values, each in the documented range
+/// <c>0..32766</c> (center 16383). Output of <see cref="AxisCalibrator"/>; fed to
+/// the virtual HID device (<c>HID_USAGE_X..RZ</c> in the legacy).
+/// </summary>
+public readonly struct AxisOutputs
+{
+    /// <summary>Documented axis range maximum (legacy uses 0..32766).</summary>
+    public const int Max = 32766;
+
+    /// <summary>Documented axis center value.</summary>
+    public const int Center = 16383;
+
+    public int X { get; }
+    public int Y { get; }
+    public int Z { get; }
+    public int Rx { get; }
+    public int Ry { get; }
+    public int Rz { get; }
+
+    public AxisOutputs(int x, int y, int z, int rx, int ry, int rz)
+    {
+        X = x;
+        Y = y;
+        Z = z;
+        Rx = rx;
+        Ry = ry;
+        Rz = rz;
+    }
+
+    public override string ToString() => $"X:{X} Y:{Y} Z:{Z} Rx:{Rx} Ry:{Ry} Rz:{Rz}";
+}
+
+/// <summary>The six virtual-joystick axes.</summary>
+public enum JoyAxis
+{
+    X,
+    Y,
+    Z,
+    Rx,
+    Ry,
+    Rz,
+}
diff --git a/src/RioJoy.Core/Mapping/OutputSinks.cs b/src/RioJoy.Core/Mapping/OutputSinks.cs
index 29e4c5e..4f1491d 100644
--- a/src/RioJoy.Core/Mapping/OutputSinks.cs
+++ b/src/RioJoy.Core/Mapping/OutputSinks.cs
@@ -66,13 +66,16 @@ public interface IInputSink
 
 /// <summary>
 /// Virtual joystick output (the HID feeder → RioGamepad driver in Phase 1).
-/// Button numbers are 0-based into the 96-button report; the hat is the single POV.
+/// Button numbers are 0-based into the 96-button report; the hat is the single POV;
+/// axis values are in the range <c>0..32766</c> (see <c>AxisOutputs</c>).
 /// </summary>
 public interface IJoystickSink
 {
     void SetButton(int button, bool pressed);
 
     void SetHat(RioHat position);
+
+    void SetAxis(Calibration.JoyAxis axis, int value);
 }
 
 /// <summary>Lamp (lighted-button) feedback, sent back to the RIO over serial.</summary>
diff --git a/src/RioJoy.Core/Plasma/PlasmaCommands.cs b/src/RioJoy.Core/Plasma/PlasmaCommands.cs
new file mode 100644
index 0000000..4f3fe0c
--- /dev/null
+++ b/src/RioJoy.Core/Plasma/PlasmaCommands.cs
@@ -0,0 +1,97 @@
+using System.Text;
+
+namespace RioJoy.Core.Plasma;
+
+/// <summary>A glyph cell size in pixels (width × height).</summary>
+public readonly record struct FontSize(int Width, int Height);
+
+/// <summary>
+/// Builds the ESC-based command byte sequences for the plasma / VFD text display
+/// on the secondary COM port. Pure port of the <c>CPlasma</c> command methods
+/// (riovjoy2.cpp#L2146); see docs/PROTOCOL.md §7. Text is encoded as Latin-1
+/// (each char → one byte), matching the legacy 8-bit <c>char*</c> packets.
+/// </summary>
+public static class PlasmaCommands
+{
+    /// <summary>The ESC lead byte (legacy <c>#define ESC 27</c>).</summary>
+    public const byte Esc = 27;
+
+    /// <summary>Clear the display (<c>ESC @</c>).</summary>
+    public static byte[] Clear() => new[] { Esc, (byte)'@' };
+
+    /// <summary>Move the cursor home (<c>ESC L</c>).</summary>
+    public static byte[] CursorHome() => new[] { Esc, (byte)'L' };
+
+    /// <summary>Set cursor cell (<c>ESC G n</c>).</summary>
+    public static byte[] Cursor(byte n) => new[] { Esc, (byte)'G', n };
+
+    /// <summary>Set cursor X (<c>ESC R x</c>).</summary>
+    public static byte[] CursorX(byte x) => new[] { Esc, (byte)'R', x };
+
+    /// <summary>Set cursor Y (<c>ESC Q y</c>).</summary>
+    public static byte[] CursorY(byte y) => new[] { Esc, (byte)'Q', y };
+
+    /// <summary>Set font attribute (<c>ESC H attr</c>).</summary>
+    public static byte[] FontAttr(byte attr) => new[] { Esc, (byte)'H', attr };
+
+    /// <summary>Select font (<c>ESC K font</c>).</summary>
+    public static byte[] Font(byte font) => new[] { Esc, (byte)'K', font };
+
+    /// <summary>Draw a box outline (<c>ESC X l t r b</c>).</summary>
+    public static byte[] BoxDraw(byte left, byte top, byte right, byte bottom) =>
+        new[] { Esc, (byte)'X', left, top, right, bottom };
+
+    /// <summary>Fill a box (<c>ESC x 0 l t r b</c>).</summary>
+    public static byte[] BoxFill(byte left, byte top, byte right, byte bottom) =>
+        new[] { Esc, (byte)'x', (byte)0, left, top, right, bottom };
+
+    /// <summary>Encode display text as raw bytes (Latin-1, one byte per char).</summary>
+    public static byte[] Text(string text)
+    {
+        ArgumentNullException.ThrowIfNull(text);
+        return Encoding.Latin1.GetBytes(text);
+    }
+
+    /// <summary>
+    /// Glyph cell size for a font id. Port of <c>GetFontSize</c> (riovjoy2.cpp#L2198):
+    /// fonts 0–3 and 6–7 are 5×7, fonts 4–5 are 10×14.
+    /// </summary>
+    public static FontSize GetFontSize(int font) => font switch
+    {
+        4 or 5 => new FontSize(10, 14),
+        _ => new FontSize(5, 7),
+    };
+
+    /// <summary>
+    /// Compute the auto-fit font and centered (x, y) for positioned text, porting
+    /// the <c>PlasmaPosText</c> layout logic (riovjoy2.cpp#L2235). For non-score
+    /// text (<paramref name="font"/> ≠ 2), the font is chosen from the length
+    /// (≤9 → font 5, else font 2, capping length at 20). When the caller passes
+    /// (0, 0), the text is centered around cell (56, 15) for the chosen font.
+    /// </summary>
+    public static (byte x, byte y, byte font, int length) ResolvePosText(
+        string text, byte x, byte y, byte font)
+    {
+        ArgumentNullException.ThrowIfNull(text);
+        int len = text.Length;
+
+        if (font != 2) // not the Score font
+        {
+            if (len <= 9) font = 5;
+            else { font = 2; if (len > 20) len = 20; }
+        }
+        else if (len > 20)
+        {
+            len = 20;
+        }
+
+        if (x == 0 && y == 0)
+        {
+            FontSize size = GetFontSize(font);
+            x = (byte)(56 - (len * size.Width / 2));
+            y = (byte)(15 - (size.Height / 2));
+        }
+
+        return (x, y, font, len);
+    }
+}
diff --git a/src/RioJoy.Core/Plasma/PlasmaDisplay.cs b/src/RioJoy.Core/Plasma/PlasmaDisplay.cs
new file mode 100644
index 0000000..3e8fe69
--- /dev/null
+++ b/src/RioJoy.Core/Plasma/PlasmaDisplay.cs
@@ -0,0 +1,52 @@
+using RioJoy.Core.Serial;
+
+namespace RioJoy.Core.Plasma;
+
+/// <summary>
+/// Drives the plasma / VFD text display over its (secondary) serial transport,
+/// writing the ESC sequences built by <see cref="PlasmaCommands"/>. Thin async
+/// wrapper around an <see cref="IRioTransport"/>; the display is write-only. The
+/// content shown is per-profile (Phase 5+).
+/// </summary>
+public sealed class PlasmaDisplay
+{
+    private readonly IRioTransport _transport;
+
+    public PlasmaDisplay(IRioTransport transport)
+    {
+        _transport = transport ?? throw new ArgumentNullException(nameof(transport));
+    }
+
+    public Task ClearAsync(CancellationToken ct = default) =>
+        WriteAsync(PlasmaCommands.Clear(), ct);
+
+    public Task CursorHomeAsync(CancellationToken ct = default) =>
+        WriteAsync(PlasmaCommands.CursorHome(), ct);
+
+    public Task TextAsync(string text, CancellationToken ct = default) =>
+        WriteAsync(PlasmaCommands.Text(text), ct);
+
+    /// <summary>
+    /// Position the cursor, set attribute + font, and write text — the
+    /// <c>PlasmaPosText</c> sequence (auto-fit via
+    /// <see cref="PlasmaCommands.ResolvePosText"/>). Pass (0,0) to auto-center.
+    /// </summary>
+    public async Task PosTextAsync(
+        string text, byte x = 0, byte y = 0, byte attr = 0, byte font = 0,
+        CancellationToken ct = default)
+    {
+        if (string.IsNullOrEmpty(text))
+            return;
+
+        (byte rx, byte ry, byte rfont, int len) = PlasmaCommands.ResolvePosText(text, x, y, font);
+
+        await WriteAsync(PlasmaCommands.CursorX(rx), ct).ConfigureAwait(false);
+        await WriteAsync(PlasmaCommands.CursorY(ry), ct).ConfigureAwait(false);
+        await WriteAsync(PlasmaCommands.FontAttr(attr), ct).ConfigureAwait(false);
+        await WriteAsync(PlasmaCommands.Font(rfont), ct).ConfigureAwait(false);
+        await WriteAsync(PlasmaCommands.Text(text[..len]), ct).ConfigureAwait(false);
+    }
+
+    private Task WriteAsync(byte[] data, CancellationToken ct) =>
+        _transport.WriteAsync(data, ct).AsTask();
+}
diff --git a/tests/RioJoy.Core.Tests/Calibration/AxisCalibratorTests.cs b/tests/RioJoy.Core.Tests/Calibration/AxisCalibratorTests.cs
new file mode 100644
index 0000000..b8e1456
--- /dev/null
+++ b/tests/RioJoy.Core.Tests/Calibration/AxisCalibratorTests.cs
@@ -0,0 +1,118 @@
+using RioJoy.Core.Calibration;
+using RioJoy.Core.Protocol;
+using Xunit;
+
+namespace RioJoy.Core.Tests.Calibration;
+
+public class AxisCalibratorTests
+{
+    // AnalogReport(throttle, leftPedal, rightPedal, joystickY, joystickX)
+    private static AnalogReport Report(
+        short throttle = 0, short left = 0, short right = 0, short y = 0, short x = 0) =>
+        new(throttle, left, right, y, x);
+
+    // --- Throttle (Z) --------------------------------------------------------
+
+    [Fact]
+    public void Throttle_BelowStart_IsProportional()
+    {
+        var cal = new AxisCalibrator();
+        cal.ResetThrottle();
+
+        // At-rest after reset: throttle equals its tracked start ⇒ centered at 0.
+        Assert.Equal(0, cal.Update(Report(throttle: 0)).Z);
+
+        // Pulled back 400 of 800 → half range × 32 = 16000.
+        Assert.Equal(16000, cal.Update(Report(throttle: -400)).Z);
+
+        // Full back (800) → 32000.
+        Assert.Equal(32000, cal.Update(Report(throttle: -800)).Z);
+    }
+
+    [Fact]
+    public void Throttle_OutOfRange_Saturates()
+    {
+        Assert.Equal(0, new AxisCalibrator().Update(Report(throttle: 900)).Z);       // > +range
+        Assert.Equal(32000, new AxisCalibrator().Update(Report(throttle: -900)).Z);  // < -range
+    }
+
+    [Fact]
+    public void Throttle_Invert_Flips()
+    {
+        var cal = new AxisCalibrator(new AxisCalibrationConfig { InvertZ = true });
+        // throttle=900 → raw 0 → inverted to Max.
+        Assert.Equal(AxisOutputs.Max, cal.Update(Report(throttle: 900)).Z);
+    }
+
+    // --- Pedals (Rx / Ry / Rz) ----------------------------------------------
+
+    [Fact]
+    public void Pedals_EnableZR_CentersRxRy_AndMixesRudder()
+    {
+        var cal = new AxisCalibrator(); // EnableZR default true
+        AxisOutputs o = cal.Update(Report(left: 0, right: 0));
+
+        Assert.Equal(AxisOutputs.Center, o.Rx);
+        Assert.Equal(AxisOutputs.Center, o.Ry);
+        Assert.Equal(AxisOutputs.Center, o.Rz); // rudder with both pedals at rest
+    }
+
+    [Fact]
+    public void Pedals_DisableZR_DriveRxDirectly_AndCenterRz()
+    {
+        var cal = new AxisCalibrator(new AxisCalibrationConfig { EnableZR = false });
+
+        // First sample sets the auto-range start; second (less depressed) produces a value.
+        cal.Update(Report(left: -100));
+        AxisOutputs o = cal.Update(Report(left: 0));
+
+        // lP = (-100) - 0 = -100 → ×1000/500 = -200 → |·|×32 = 6400.
+        Assert.Equal(6400, o.Rx);
+        Assert.Equal(AxisOutputs.Center, o.Rz); // Rz centered when ZR disabled
+    }
+
+    // --- Joystick (X / Y) ----------------------------------------------------
+
+    [Fact]
+    public void Joystick_AtZero_IsCentered()
+    {
+        AxisOutputs o = new AxisCalibrator().Update(Report(x: 0, y: 0));
+        Assert.Equal(AxisOutputs.Center, o.X);
+        Assert.Equal(AxisOutputs.Center, o.Y);
+    }
+
+    [Fact]
+    public void JoystickX_RightAndLeft_MoveOppositeSidesOfCenter()
+    {
+        // Right (positive raw) → below center; with auto-range seeded by this sample.
+        Assert.Equal(52, new AxisCalibrator().Update(Report(x: 80)).X);
+        // Left (negative raw) → above center.
+        Assert.Equal(32733, new AxisCalibrator().Update(Report(x: -80)).X);
+    }
+
+    [Fact]
+    public void JoystickX_Invert_Flips()
+    {
+        var cal = new AxisCalibrator(new AxisCalibrationConfig { InvertX = true });
+        Assert.Equal(AxisOutputs.Max - 52, cal.Update(Report(x: 80)).X);
+    }
+
+    [Fact]
+    public void ResetHorizontalJoystick_RecentersX()
+    {
+        var cal = new AxisCalibrator();
+        Assert.Equal(52, cal.Update(Report(x: 80)).X);
+
+        cal.ResetHorizontalJoystick();
+        // After reset, X holds center until the stick next moves off zero.
+        Assert.Equal(AxisOutputs.Center, cal.Update(Report(x: 0)).X);
+    }
+
+    [Fact]
+    public void Outputs_AreClampedToAxisRange()
+    {
+        // The init-state throttle quirk yields a value far over range on the first
+        // poll at rest; the documented 0..Max clamp guards it.
+        Assert.Equal(AxisOutputs.Max, new AxisCalibrator().Update(Report(throttle: 0)).Z);
+    }
+}
diff --git a/tests/RioJoy.Core.Tests/Mapping/RecordingSink.cs b/tests/RioJoy.Core.Tests/Mapping/RecordingSink.cs
index dd96593..3d921b5 100644
--- a/tests/RioJoy.Core.Tests/Mapping/RecordingSink.cs
+++ b/tests/RioJoy.Core.Tests/Mapping/RecordingSink.cs
@@ -22,6 +22,8 @@ internal sealed class RecordingSink : IInputSink, IJoystickSink, ILampSink, IRio
 
     public void SetHat(RioHat position) => Log.Add($"Hat({position})");
 
+    public void SetAxis(RioJoy.Core.Calibration.JoyAxis axis, int value) => Log.Add($"Axis({axis},{value})");
+
     public void SetLamp(int address, byte lampState) => Log.Add($"Lamp(0x{address:X2},0x{lampState:X2})");
 
     public void Execute(RioCommandCode command) => Log.Add($"Cmd({command})");
diff --git a/tests/RioJoy.Core.Tests/Plasma/PlasmaCommandsTests.cs b/tests/RioJoy.Core.Tests/Plasma/PlasmaCommandsTests.cs
new file mode 100644
index 0000000..65a280e
--- /dev/null
+++ b/tests/RioJoy.Core.Tests/Plasma/PlasmaCommandsTests.cs
@@ -0,0 +1,76 @@
+using RioJoy.Core.Plasma;
+using Xunit;
+
+namespace RioJoy.Core.Tests.Plasma;
+
+public class PlasmaCommandsTests
+{
+    [Fact]
+    public void EscSequences_AreCorrect()
+    {
+        Assert.Equal(new byte[] { 27, (byte)'@' }, PlasmaCommands.Clear());
+        Assert.Equal(new byte[] { 27, (byte)'L' }, PlasmaCommands.CursorHome());
+        Assert.Equal(new byte[] { 27, (byte)'R', 10 }, PlasmaCommands.CursorX(10));
+        Assert.Equal(new byte[] { 27, (byte)'Q', 20 }, PlasmaCommands.CursorY(20));
+        Assert.Equal(new byte[] { 27, (byte)'H', 3 }, PlasmaCommands.FontAttr(3));
+        Assert.Equal(new byte[] { 27, (byte)'K', 5 }, PlasmaCommands.Font(5));
+    }
+
+    [Fact]
+    public void Box_DrawAndFill_HaveExpectedLayout()
+    {
+        Assert.Equal(new byte[] { 27, (byte)'X', 1, 2, 3, 4 }, PlasmaCommands.BoxDraw(1, 2, 3, 4));
+        // Fill inserts a leading 0 parameter.
+        Assert.Equal(new byte[] { 27, (byte)'x', 0, 1, 2, 3, 4 }, PlasmaCommands.BoxFill(1, 2, 3, 4));
+    }
+
+    [Fact]
+    public void Text_EncodesOneBytePerChar()
+    {
+        Assert.Equal(new byte[] { (byte)'A', (byte)'B', (byte)'C' }, PlasmaCommands.Text("ABC"));
+    }
+
+    [Theory]
+    [InlineData(0, 5, 7)]
+    [InlineData(3, 5, 7)]
+    [InlineData(4, 10, 14)]
+    [InlineData(5, 10, 14)]
+    [InlineData(7, 5, 7)]
+    public void GetFontSize_MatchesLegacy(int font, int w, int h)
+    {
+        Assert.Equal(new FontSize(w, h), PlasmaCommands.GetFontSize(font));
+    }
+
+    [Fact]
+    public void ResolvePosText_ShortText_PicksFont5_AndCenters()
+    {
+        // "HELLO" (5) is non-score and ≤9 → font 5 (10×14). Centered around (56,15).
+        (byte x, byte y, byte font, int len) = PlasmaCommands.ResolvePosText("HELLO", 0, 0, 0);
+        Assert.Equal(5, font);
+        Assert.Equal(5, len);
+        Assert.Equal(31, x); // 56 - (5*10/2)
+        Assert.Equal(8, y);  // 15 - (14/2)
+    }
+
+    [Fact]
+    public void ResolvePosText_LongText_Font2_AndCapsLength()
+    {
+        string text = new string('1', 24);
+        (byte x, byte y, byte font, int len) = PlasmaCommands.ResolvePosText(text, 0, 0, 0);
+        Assert.Equal(2, font);
+        Assert.Equal(20, len); // capped
+        Assert.Equal(6, x);    // 56 - (20*5/2)
+        Assert.Equal(12, y);   // 15 - (7/2)
+    }
+
+    [Fact]
+    public void ResolvePosText_ScoreFont_AndExplicitPosition_Unchanged()
+    {
+        // font 2 (score) keeps its font; non-zero position is not re-centered.
+        (byte x, byte y, byte font, int len) = PlasmaCommands.ResolvePosText("AB", 5, 6, 2);
+        Assert.Equal(2, font);
+        Assert.Equal(2, len);
+        Assert.Equal(5, x);
+        Assert.Equal(6, y);
+    }
+}