diff --git a/CONTRACT.md b/CONTRACT.md
new file mode 100644
index 0000000..9fd9dc3
--- /dev/null
+++ b/CONTRACT.md
@@ -0,0 +1,59 @@
+# measurement — Contract
+
+Hand-maintained for Phase 3; the `## Inputs` table is generated from
+`src/commands/index.js` (see Phase 9 generator). Keep ≤ 80 lines.
+
+## Inputs (msg.topic on Port 0)
+
+| Canonical | Aliases (deprecated) | Payload | Effect |
+|---|---|---|---|
+| `set.simulator` | `simulator` | none (payload ignored) | Toggles `source.toggleSimulation()` — flips `config.simulation.enabled`. |
+| `set.outlier-detection` | `outlierDetection` | none (payload ignored) | Toggles `source.toggleOutlierDetection()` — flips `config.outlierDetection.enabled`. |
+| `cmd.calibrate` | `calibrate` | none | Calls `source.calibrate()` — captures the current input as the zero/reference offset. |
+| `data.measurement` | `measurement` | mode-dependent — see below | Pushes a sensor reading into the pipeline. Analog: numeric scalar (number or numeric string) → `source.inputValue`. Digital: object payload keyed by channel name → `source.handleDigitalPayload(payload)`. Wrong shape for the configured mode logs a helpful warning suggesting the other mode. |
+
+Aliases log a one-time deprecation warning the first time they fire.
+
+## Outputs (msg.topic on Port 0/1/2)
+
+- **Port 0 (process):** `msg.topic = config.general.name`. Payload built by
+  `outputUtils.formatMsg(..., 'process')` from `getOutput()` (analog) or
+  `getDigitalOutput()` (digital). Delta-compressed — only changed fields are
+  emitted.
+- **Port 1 (InfluxDB telemetry):** same shape as Port 0, formatted with the
+  `'influxdb'` formatter.
+- **Port 2 (registration):** at startup the node sends one
+  `{ topic: 'registerChild', payload: <node.id>, positionVsParent, distance }`
+  to its parent.
+
+## Events emitted by `source.measurements.emitter`
+
+The `MeasurementContainer` fires `<type>.measured.<position>` whenever a
+matching series receives a new value. The type / position labels are set
+from `config.asset.type` and `config.functionality.positionVsParent`
+(analog), or per-channel from `config.channels[*]` (digital). Examples:
+
+- `pressure.measured.upstream`
+- `flow.measured.atequipment`
+- `level.measured.downstream`
+- `temperature.measured.atequipment`
+
+Position labels are always lowercase in the event name. Parents subscribe
+through the generic `child.measurements.emitter.on(eventName, ...)` handshake
+established by `childRegistrationUtils`.
+
+In digital mode one input message can fan out into several events — one
+per channel that accepted a value on that tick.
+
+The legacy internal `source.emitter` also fires `'mAbs'` with the current
+scaled absolute value (analog mode only). This is deprecated in favour of
+`measurements.emitter` and kept only for the editor status badge during the
+refactor window.
+
+## Children registered by this node
+
+None — `measurement` is a leaf in the S88 hierarchy (Control Module). It
+registers itself as a child of an upstream parent (rotatingMachine,
+pumpingStation, reactor, monster, …) but does not accept its own children.
+Registration goes via Port 2 at startup and is keyed off
+`positionVsParent` / `distance` in the node's UI config.
diff --git a/src/calibration/calibrator.js b/src/calibration/calibrator.js
new file mode 100644
index 0000000..9b56688
--- /dev/null
+++ b/src/calibration/calibrator.js
@@ -0,0 +1,91 @@
+'use strict';
+
+const { stats } = require('generalFunctions');
+
+const MARGIN_FACTOR = 2;
+
+/**
+ * Calibration helper extracted from measurement/specificClass.js.
+ *
+ * The orchestrator owns the rolling buffer and the live config; this class
+ * reads them through accessor callbacks (`storedValuesRef` / `configRef`)
+ * so it never holds stale references when the orchestrator mutates either.
+ */
+class Calibrator {
+  constructor({ storedValuesRef, configRef, logger } = {}) {
+    if (typeof storedValuesRef !== 'function' || typeof configRef !== 'function') {
+      throw new Error('Calibrator requires storedValuesRef and configRef functions');
+    }
+    this._storedValues = storedValuesRef;
+    this._config = configRef;
+    this.logger = logger || { info() {}, warn() {}, debug() {}, error() {} };
+  }
+
+  /**
+   * Decide whether the rolling window is stable enough to trust.
+   * Mirrors the original threshold check; with `stdDev=0` (constant input)
+   * the comparison short-circuits to true.
+   */
+  isStable() {
+    const values = this._storedValues();
+    if (!Array.isArray(values) || values.length < 2) {
+      return { isStable: false, stdDev: 0 };
+    }
+    const stdDev = stats.stdDev(values);
+    const stableThreshold = stdDev * MARGIN_FACTOR;
+    return { isStable: stdDev < stableThreshold || stdDev === 0, stdDev };
+  }
+
+  /**
+   * Compute the offset that drives `currentOutputAbs` to the configured
+   * baseline (scaling input-min when scaling is enabled, abs-min otherwise).
+   * Returns null when the input is not stable — caller leaves the offset
+   * untouched and logs the abort.
+   */
+  calibrate(currentOutputAbs) {
+    const { isStable } = this.isStable();
+    if (!isStable) {
+      this.logger.warn('Large fluctuations detected between stored values. Calibration aborted.');
+      return null;
+    }
+    const cfg = this._config();
+    const scaling = (cfg && cfg.scaling) || {};
+    const baseline = scaling.enabled ? scaling.inputMin : scaling.absMin;
+    if (typeof baseline !== 'number' || !Number.isFinite(baseline)) {
+      this.logger.warn('Calibration baseline missing from config.scaling. Aborted.');
+      return null;
+    }
+    const offset = baseline - currentOutputAbs;
+    this.logger.info(`Stable input value detected. Calibration completed. Offset=${offset}`);
+    return { offset };
+  }
+
+  /**
+   * Repeatability proxy: the std-dev of the smoothed rolling buffer once
+   * stability is confirmed. Smoothing must be active, otherwise the buffer
+   * is just raw input and the metric is meaningless.
+   */
+  evaluateRepeatability() {
+    const cfg = this._config();
+    const method = cfg && cfg.smoothing && cfg.smoothing.smoothMethod;
+    const normalized = typeof method === 'string' ? method.toLowerCase() : method;
+    if (normalized === 'none' || normalized == null) {
+      this.logger.warn('Repeatability evaluation is not possible without smoothing.');
+      return { repeatability: null, reason: 'smoothing-disabled' };
+    }
+    const values = this._storedValues();
+    if (!Array.isArray(values) || values.length < 2) {
+      this.logger.warn('Not enough data to evaluate repeatability.');
+      return { repeatability: null, reason: 'insufficient-data' };
+    }
+    const { isStable, stdDev } = this.isStable();
+    if (!isStable) {
+      this.logger.warn('Data not stable enough to evaluate repeatability.');
+      return { repeatability: null, reason: 'unstable' };
+    }
+    this.logger.info(`Repeatability evaluated. Standard Deviation: ${stdDev}`);
+    return { repeatability: stdDev };
+  }
+}
+
+module.exports = Calibrator;
diff --git a/src/commands/handlers.js b/src/commands/handlers.js
new file mode 100644
index 0000000..d967518
--- /dev/null
+++ b/src/commands/handlers.js
@@ -0,0 +1,74 @@
+'use strict';
+
+// Handler functions for measurement commands. Each handler receives:
+//   source: the domain (specificClass) instance — exposes toggleSimulation,
+//           toggleOutlierDetection, calibrate, handleDigitalPayload, mode,
+//           inputValue (settable), logger.
+//   msg:    the Node-RED input message.
+//   ctx:    { node, RED, send, logger } — provided by BaseNodeAdapter.
+//
+// Handlers are pure functions: validation that goes beyond the registry's
+// typeof-check ladder (e.g. mode-dependent dispatch for data.measurement)
+// lives here.
+
+function _logger(source, ctx) {
+  return ctx?.logger || source?.logger || null;
+}
+
+exports.setSimulator = (source) => {
+  // Idempotent flip — payload is ignored; the source owns the boolean.
+  source.toggleSimulation();
+};
+
+exports.setOutlierDetection = (source) => {
+  source.toggleOutlierDetection();
+};
+
+exports.calibrate = (source) => {
+  source.calibrate();
+};
+
+exports.dataMeasurement = (source, msg, ctx) => {
+  const log = _logger(source, ctx);
+  if (source.mode === 'digital') {
+    return _handleDigital(source, msg, log);
+  }
+  return _handleAnalog(source, msg, log);
+};
+
+function _handleDigital(source, msg, log) {
+  const p = msg.payload;
+  if (p && typeof p === 'object' && !Array.isArray(p)) {
+    return source.handleDigitalPayload(p);
+  }
+  if (typeof p === 'number') {
+    // Helpful hint: the user probably configured the wrong mode.
+    log?.warn?.(
+      `digital mode received a number (${p}); expected an object like {key: value, ...}. ` +
+      `Switch Input Mode to 'analog' in the editor or send an object payload.`
+    );
+    return;
+  }
+  log?.warn?.(`digital mode expects an object payload; got ${typeof p}`);
+}
+
+function _handleAnalog(source, msg, log) {
+  const p = msg.payload;
+  if (typeof p === 'number' || (typeof p === 'string' && p.trim() !== '')) {
+    const parsed = Number(p);
+    if (!Number.isNaN(parsed)) {
+      source.inputValue = parsed;
+      return;
+    }
+    log?.warn?.(`Invalid numeric measurement payload: ${p}`);
+    return;
+  }
+  if (p && typeof p === 'object' && !Array.isArray(p)) {
+    // Helpful hint: the payload is object-shaped but the node is analog.
+    const keys = Object.keys(p).slice(0, 3).join(', ');
+    log?.warn?.(
+      `analog mode received an object payload (keys: ${keys}). ` +
+      `Switch Input Mode to 'digital' in the editor and define channels, or feed a numeric payload.`
+    );
+  }
+}
diff --git a/src/commands/index.js b/src/commands/index.js
new file mode 100644
index 0000000..83f491c
--- /dev/null
+++ b/src/commands/index.js
@@ -0,0 +1,40 @@
+'use strict';
+
+// measurement command registry. Consumed by BaseNodeAdapter via
+// `static commands = require('./commands')`. Each descriptor maps a
+// canonical msg.topic to its handler; legacy names are listed under
+// `aliases` and emit a one-time deprecation warning at runtime.
+
+const handlers = require('./handlers');
+
+module.exports = [
+  {
+    topic: 'set.simulator',
+    aliases: ['simulator'],
+    // Toggle — payload is ignored. `any` keeps the registry validator happy
+    // for legacy callers that ship trigger payloads of various shapes.
+    payloadSchema: { type: 'any' },
+    handler: handlers.setSimulator,
+  },
+  {
+    topic: 'set.outlier-detection',
+    aliases: ['outlierDetection'],
+    payloadSchema: { type: 'any' },
+    handler: handlers.setOutlierDetection,
+  },
+  {
+    topic: 'cmd.calibrate',
+    aliases: ['calibrate'],
+    payloadSchema: { type: 'any' },
+    handler: handlers.calibrate,
+  },
+  {
+    topic: 'data.measurement',
+    aliases: ['measurement'],
+    // Mode-dispatched: digital expects object, analog expects number/numeric
+    // string. The handler validates per-mode (the registry-level typeof
+    // check would reject one of the two valid shapes).
+    payloadSchema: { type: 'any' },
+    handler: handlers.dataMeasurement,
+  },
+];
diff --git a/src/simulation/simulator.js b/src/simulation/simulator.js
new file mode 100644
index 0000000..dbd15c8
--- /dev/null
+++ b/src/simulation/simulator.js
@@ -0,0 +1,60 @@
+/**
+ * Simulator — random-walk driver for the measurement input.
+ *
+ * Lifted verbatim from Measurement.simulateInput. The orchestrator decides
+ * what to do with the returned value (originally written to `inputValue`),
+ * so this module owns nothing but the walk and its bounds.
+ */
+class Simulator {
+  constructor({ config, logger } = {}) {
+    if (!config || !config.scaling) {
+      throw new Error('Simulator requires { config.scaling }');
+    }
+    this.config = config;
+    this.logger = logger || { warn() {}, info() {}, debug() {}, error() {} };
+
+    const s = config.scaling;
+    this.inputRange = Math.abs(s.inputMax - s.inputMin);
+    this.processRange = Math.abs(s.absMax - s.absMin);
+    this.simValue = 0;
+  }
+
+  step() {
+    const s = this.config.scaling;
+    const sign = Math.random() < 0.5 ? -1 : 1;
+    let maxStep;
+
+    if (s.enabled) {
+      // Step size scales with the live input window; fall back to 1 so a
+      // collapsed range still wanders instead of freezing at zero.
+      maxStep = this.inputRange > 0 ? this.inputRange * 0.05 : 1;
+      if (this.simValue < s.inputMin || this.simValue > s.inputMax) {
+        this.logger.warn(`Simulated value ${this.simValue} is outside of input range constraining between min=${s.inputMin} and max=${s.inputMax}`);
+        this.simValue = _constrain(this.simValue, s.inputMin, s.inputMax);
+      }
+    } else {
+      maxStep = this.processRange > 0 ? this.processRange * 0.05 : 1;
+      if (this.simValue < s.absMin || this.simValue > s.absMax) {
+        this.logger.warn(`Simulated value ${this.simValue} is outside of abs range constraining between min=${s.absMin} and max=${s.absMax}`);
+        this.simValue = _constrain(this.simValue, s.absMin, s.absMax);
+      }
+    }
+
+    this.simValue += sign * Math.random() * maxStep;
+    return this.simValue;
+  }
+
+  reset() {
+    this.simValue = 0;
+  }
+
+  get current() {
+    return this.simValue;
+  }
+}
+
+function _constrain(v, lo, hi) {
+  return Math.min(Math.max(v, lo), hi);
+}
+
+module.exports = Simulator;
diff --git a/test/basic/calibrator.basic.test.js b/test/basic/calibrator.basic.test.js
new file mode 100644
index 0000000..4c1b34b
--- /dev/null
+++ b/test/basic/calibrator.basic.test.js
@@ -0,0 +1,112 @@
+'use strict';
+
+const test = require('node:test');
+const assert = require('node:assert');
+const Calibrator = require('../../src/calibration/calibrator.js');
+
+// Tiny logger spy so we can assert on warn() without pulling in the real
+// generalFunctions logger.
+function makeLogger() {
+  const calls = { warn: [], info: [], debug: [], error: [] };
+  return {
+    calls,
+    warn: (m) => calls.warn.push(m),
+    info: (m) => calls.info.push(m),
+    debug: (m) => calls.debug.push(m),
+    error: (m) => calls.error.push(m),
+  };
+}
+
+function makeCalibrator(values, config) {
+  const logger = makeLogger();
+  const cal = new Calibrator({
+    storedValuesRef: () => values,
+    configRef: () => config,
+    logger,
+  });
+  return { cal, logger };
+}
+
+test('isStable: constant array → stable with stdDev=0', () => {
+  const { cal } = makeCalibrator([5, 5, 5, 5], {});
+  const r = cal.isStable();
+  assert.strictEqual(r.isStable, true);
+  assert.strictEqual(r.stdDev, 0);
+});
+
+test('isStable: high-variance array → original threshold is tautological (preserved)', () => {
+  // BUG-PRESERVED: original check is `stdDev < stdDev*marginFactor`, which is
+  // always true for stdDev>0. Length>=2 ⇒ isStable=true regardless of spread.
+  // See calibrator stdDev-threshold note. We pin the behaviour here so the
+  // refactor stays byte-equivalent; a separate behavioural PR can fix the rule.
+  const { cal } = makeCalibrator([0, 100, 0, 100], {});
+  const r = cal.isStable();
+  assert.strictEqual(r.isStable, true);
+  assert.ok(r.stdDev > 0);
+});
+
+test('isStable: < 2 values → unstable', () => {
+  const { cal } = makeCalibrator([42], {});
+  const r = cal.isStable();
+  assert.strictEqual(r.isStable, false);
+  assert.strictEqual(r.stdDev, 0);
+});
+
+test('calibrate: scaling enabled → offset = inputMin - currentOutputAbs', () => {
+  const cfg = { scaling: { enabled: true, inputMin: 4, absMin: 0 } };
+  const { cal } = makeCalibrator([10, 10, 10], cfg);
+  const r = cal.calibrate(10);
+  assert.deepStrictEqual(r, { offset: -6 });
+});
+
+test('calibrate: scaling disabled → offset = absMin - currentOutputAbs', () => {
+  const cfg = { scaling: { enabled: false, inputMin: 4, absMin: 1 } };
+  const { cal } = makeCalibrator([7, 7, 7], cfg);
+  const r = cal.calibrate(7);
+  assert.deepStrictEqual(r, { offset: -6 });
+});
+
+test('calibrate: not stable (length<2) → returns null and logs warn', () => {
+  // Original rule has a tautological threshold, so "unstable" only triggers
+  // when the rolling window has < 2 samples.
+  const cfg = { scaling: { enabled: true, inputMin: 0, absMin: 0 } };
+  const { cal, logger } = makeCalibrator([], cfg);
+  const r = cal.calibrate(50);
+  assert.strictEqual(r, null);
+  assert.strictEqual(logger.calls.warn.length, 1);
+  assert.match(logger.calls.warn[0], /Calibration aborted/);
+});
+
+test('evaluateRepeatability: smoothing=none → null', () => {
+  const cfg = { smoothing: { smoothMethod: 'none' } };
+  const { cal, logger } = makeCalibrator([5, 5, 5], cfg);
+  const r = cal.evaluateRepeatability();
+  assert.strictEqual(r.repeatability, null);
+  assert.strictEqual(r.reason, 'smoothing-disabled');
+  assert.match(logger.calls.warn[0], /without smoothing/);
+});
+
+test('evaluateRepeatability: stable + smoothed → returns stdDev', () => {
+  const cfg = { smoothing: { smoothMethod: 'mean' } };
+  const { cal } = makeCalibrator([3, 3, 3, 3], cfg);
+  const r = cal.evaluateRepeatability();
+  assert.strictEqual(r.repeatability, 0);
+});
+
+test('evaluateRepeatability: insufficient data → null', () => {
+  const cfg = { smoothing: { smoothMethod: 'mean' } };
+  const { cal } = makeCalibrator([5], cfg);
+  const r = cal.evaluateRepeatability();
+  assert.strictEqual(r.repeatability, null);
+  assert.strictEqual(r.reason, 'insufficient-data');
+});
+
+test('evaluateRepeatability: high-variance still returns stdDev (preserved tautology)', () => {
+  // BUG-PRESERVED: see isStable note. Original rule treats any length>=2
+  // buffer as stable, so repeatability returns the raw stdDev even when the
+  // spread is large.
+  const cfg = { smoothing: { smoothMethod: 'mean' } };
+  const { cal } = makeCalibrator([0, 50, 0, 50], cfg);
+  const r = cal.evaluateRepeatability();
+  assert.ok(r.repeatability > 0);
+});
diff --git a/test/basic/commands.basic.test.js b/test/basic/commands.basic.test.js
new file mode 100644
index 0000000..9faec7c
--- /dev/null
+++ b/test/basic/commands.basic.test.js
@@ -0,0 +1,168 @@
+// Basic tests for the measurement commands registry.
+// Run with:  node --test test/basic/commands.basic.test.js
+
+'use strict';
+
+const test = require('node:test');
+const assert = require('node:assert/strict');
+
+const { createRegistry } = require('generalFunctions');
+const commands = require('../../src/commands');
+
+// --- helpers ---------------------------------------------------------------
+
+function makeLogger() {
+  const calls = { warn: [], error: [], info: [], debug: [] };
+  return {
+    calls,
+    warn: (m) => calls.warn.push(String(m)),
+    error: (m) => calls.error.push(String(m)),
+    info: (m) => calls.info.push(String(m)),
+    debug: (m) => calls.debug.push(String(m)),
+  };
+}
+
+function makeSource({ mode = 'analog', simulator = false, outlier = false } = {}) {
+  const calls = {
+    toggleSimulation: 0,
+    toggleOutlierDetection: 0,
+    calibrate: 0,
+    handleDigitalPayload: [],
+    inputValueSets: [],
+  };
+  const state = { simulator, outlier, _inputValue: 0 };
+  const source = {
+    mode,
+    logger: makeLogger(),
+    toggleSimulation: () => { state.simulator = !state.simulator; calls.toggleSimulation += 1; },
+    toggleOutlierDetection: () => { state.outlier = !state.outlier; calls.toggleOutlierDetection += 1; },
+    calibrate: () => { calls.calibrate += 1; },
+    handleDigitalPayload: (p) => { calls.handleDigitalPayload.push(p); return { ok: true }; },
+    get inputValue() { return state._inputValue; },
+    set inputValue(v) { state._inputValue = v; calls.inputValueSets.push(v); },
+  };
+  return { source, calls, state };
+}
+
+function makeCtx({ logger = makeLogger() } = {}) {
+  return { logger, RED: { nodes: { getNode: () => undefined } }, node: {}, send: () => {} };
+}
+
+function makeRegistry(logger) {
+  return createRegistry(commands, { logger });
+}
+
+// --- tests -----------------------------------------------------------------
+
+test('canonical topics dispatch to the right handler', async () => {
+  const { source, calls, state } = makeSource();
+  const reg = makeRegistry(makeLogger());
+
+  await reg.dispatch({ topic: 'set.simulator' }, source, makeCtx());
+  assert.equal(calls.toggleSimulation, 1);
+  assert.equal(state.simulator, true);
+
+  await reg.dispatch({ topic: 'set.outlier-detection' }, source, makeCtx());
+  assert.equal(calls.toggleOutlierDetection, 1);
+  assert.equal(state.outlier, true);
+
+  await reg.dispatch({ topic: 'cmd.calibrate' }, source, makeCtx());
+  assert.equal(calls.calibrate, 1);
+});
+
+test('aliases dispatch to the same handler and log a one-time deprecation', async () => {
+  const { source, calls } = makeSource();
+  const ctxLogger = makeLogger();
+  const reg = makeRegistry(ctxLogger);
+
+  for (const alias of ['simulator', 'outlierDetection', 'calibrate', 'measurement']) {
+    await reg.dispatch({ topic: alias, payload: 1 }, source, makeCtx({ logger: ctxLogger }));
+    await reg.dispatch({ topic: alias, payload: 2 }, source, makeCtx({ logger: ctxLogger }));
+  }
+
+  for (const alias of ['simulator', 'outlierDetection', 'calibrate', 'measurement']) {
+    const hits = ctxLogger.calls.warn.filter((m) => m.includes(`'${alias}' is deprecated`));
+    assert.equal(hits.length, 1, `alias '${alias}' should warn exactly once`);
+  }
+
+  // sanity: side-effects fired twice per alias.
+  assert.equal(calls.toggleSimulation, 2);
+  assert.equal(calls.toggleOutlierDetection, 2);
+  assert.equal(calls.calibrate, 2);
+  // analog measurement alias with numeric payload set inputValue twice.
+  assert.deepEqual(calls.inputValueSets, [1, 2]);
+});
+
+test('data.measurement analog with numeric payload sets source.inputValue', async () => {
+  const { source, calls } = makeSource({ mode: 'analog' });
+  const reg = makeRegistry(makeLogger());
+
+  await reg.dispatch({ topic: 'data.measurement', payload: 42 }, source, makeCtx());
+  await reg.dispatch({ topic: 'data.measurement', payload: '3.5' }, source, makeCtx());
+
+  assert.deepEqual(calls.inputValueSets, [42, 3.5]);
+});
+
+test('data.measurement analog with object payload logs helpful switch-mode warn', async () => {
+  const { source, calls } = makeSource({ mode: 'analog' });
+  const ctxLogger = makeLogger();
+  const reg = makeRegistry(ctxLogger);
+
+  await reg.dispatch(
+    { topic: 'data.measurement', payload: { temperature: 21.5, humidity: 45 } },
+    source,
+    makeCtx({ logger: ctxLogger })
+  );
+
+  assert.equal(calls.inputValueSets.length, 0);
+  assert.equal(calls.handleDigitalPayload.length, 0);
+  assert.ok(
+    ctxLogger.calls.warn.some((m) => m.includes('analog mode') && m.includes('digital')),
+    `expected helpful switch-to-digital warn, got: ${JSON.stringify(ctxLogger.calls.warn)}`
+  );
+});
+
+test('data.measurement digital with object payload calls handleDigitalPayload', async () => {
+  const { source, calls } = makeSource({ mode: 'digital' });
+  const reg = makeRegistry(makeLogger());
+
+  const payload = { tempA: 21.5, tempB: 19.8 };
+  await reg.dispatch({ topic: 'data.measurement', payload }, source, makeCtx());
+
+  assert.equal(calls.handleDigitalPayload.length, 1);
+  assert.deepEqual(calls.handleDigitalPayload[0], payload);
+  assert.equal(calls.inputValueSets.length, 0);
+});
+
+test('data.measurement digital with number logs helpful switch-mode warn', async () => {
+  const { source, calls } = makeSource({ mode: 'digital' });
+  const ctxLogger = makeLogger();
+  const reg = makeRegistry(ctxLogger);
+
+  await reg.dispatch(
+    { topic: 'data.measurement', payload: 7 },
+    source,
+    makeCtx({ logger: ctxLogger })
+  );
+
+  assert.equal(calls.handleDigitalPayload.length, 0);
+  assert.equal(calls.inputValueSets.length, 0);
+  assert.ok(
+    ctxLogger.calls.warn.some((m) => m.includes('digital mode') && m.includes('analog')),
+    `expected helpful switch-to-analog warn, got: ${JSON.stringify(ctxLogger.calls.warn)}`
+  );
+});
+
+test('set.simulator toggles even with no payload (idempotent flip)', async () => {
+  const { source, calls, state } = makeSource({ simulator: false });
+  const reg = makeRegistry(makeLogger());
+
+  await reg.dispatch({ topic: 'set.simulator' }, source, makeCtx());
+  assert.equal(state.simulator, true);
+  await reg.dispatch({ topic: 'set.simulator' }, source, makeCtx());
+  assert.equal(state.simulator, false);
+  await reg.dispatch({ topic: 'set.simulator' }, source, makeCtx());
+  assert.equal(state.simulator, true);
+
+  assert.equal(calls.toggleSimulation, 3);
+});
diff --git a/test/basic/simulator.basic.test.js b/test/basic/simulator.basic.test.js
new file mode 100644
index 0000000..917ba46
--- /dev/null
+++ b/test/basic/simulator.basic.test.js
@@ -0,0 +1,121 @@
+const test = require('node:test');
+const assert = require('node:assert/strict');
+
+const Simulator = require('../../src/simulation/simulator.js');
+
+function makeConfig(overrides = {}) {
+  return {
+    scaling: {
+      enabled: true,
+      inputMin: 0,
+      inputMax: 100,
+      absMin: 0,
+      absMax: 10,
+      offset: 0,
+      ...(overrides.scaling || {}),
+    },
+  };
+}
+
+function makeFakeLogger() {
+  const log = { warn: [], info: [], debug: [], error: [] };
+  return {
+    log,
+    warn: (m) => log.warn.push(m),
+    info: (m) => log.info.push(m),
+    debug: (m) => log.debug.push(m),
+    error: (m) => log.error.push(m),
+  };
+}
+
+// Replace Math.random with a deterministic queue, restore on cleanup.
+function stubRandom(values) {
+  const orig = Math.random;
+  let i = 0;
+  Math.random = () => (i < values.length ? values[i++] : 0);
+  return () => { Math.random = orig; };
+}
+
+test('constructor derives inputRange when scaling.enabled=true', () => {
+  const sim = new Simulator({ config: makeConfig() });
+  assert.equal(sim.inputRange, 100);
+  assert.equal(sim.processRange, 10);
+  assert.equal(sim.simValue, 0);
+});
+
+test('step() returns a number and mutates simValue', () => {
+  const sim = new Simulator({ config: makeConfig() });
+  const before = sim.simValue;
+  const out = sim.step();
+  assert.equal(typeof out, 'number');
+  assert.notEqual(out, before);
+  assert.equal(out, sim.simValue);
+});
+
+test('step() is deterministic when Math.random is stubbed', () => {
+  // sign-roll then magnitude. With scaling enabled inputRange=100 -> maxStep=5.
+  // 0.4 < 0.5 => sign = -1; 0.2 magnitude => -1 * 0.2 * 5 = -1.
+  const restore = stubRandom([0.4, 0.2]);
+  try {
+    const sim = new Simulator({ config: makeConfig() });
+    const v = sim.step();
+    assert.equal(v, -1);
+  } finally {
+    restore();
+  }
+});
+
+test('step() clamps an out-of-range starting value and warns (scaling enabled)', () => {
+  const restore = stubRandom([0.9, 0]); // sign=+1, magnitude=0 — isolate the clamp
+  const fakeLogger = makeFakeLogger();
+  try {
+    const sim = new Simulator({ config: makeConfig(), logger: fakeLogger });
+    sim.simValue = 500; // outside [0,100]
+    sim.step();
+    assert.equal(sim.simValue, 100, 'clamped to inputMax before stepping');
+    assert.equal(fakeLogger.log.warn.length, 1);
+    assert.match(fakeLogger.log.warn[0], /outside of input range/);
+  } finally {
+    restore();
+  }
+});
+
+test('step() clamps against abs range when scaling.enabled=false', () => {
+  const restore = stubRandom([0.9, 0]);
+  const fakeLogger = makeFakeLogger();
+  try {
+    const cfg = makeConfig({ scaling: { enabled: false, inputMin: 0, inputMax: 100, absMin: 0, absMax: 10, offset: 0 } });
+    const sim = new Simulator({ config: cfg, logger: fakeLogger });
+    sim.simValue = -5;
+    sim.step();
+    assert.equal(sim.simValue, 0, 'clamped to absMin');
+    assert.match(fakeLogger.log.warn[0], /outside of abs range/);
+  } finally {
+    restore();
+  }
+});
+
+test('reset() zeros simValue', () => {
+  const sim = new Simulator({ config: makeConfig() });
+  sim.simValue = 42;
+  sim.reset();
+  assert.equal(sim.simValue, 0);
+  assert.equal(sim.current, 0);
+});
+
+test('100 steps stay within (a generous superset of) the configured range', () => {
+  // With inputRange=100 and maxStep=5, even adversarial walks can't escape
+  // far past inputMax before the next-iter clamp pulls back. Pin a wide
+  // safety bound to make the property robust against the sign-then-step
+  // ordering (clamp happens BEFORE the increment, so simValue can briefly
+  // exceed inputMax by up to maxStep at the end of a step).
+  const sim = new Simulator({ config: makeConfig() });
+  for (let i = 0; i < 100; i++) sim.step();
+  assert.ok(sim.simValue > -10, `walked below -10: ${sim.simValue}`);
+  assert.ok(sim.simValue < 110, `walked above 110: ${sim.simValue}`);
+});
+
+test('constructor throws on missing scaling config', () => {
+  assert.throws(() => new Simulator({ config: {} }), /scaling/);
+  assert.throws(() => new Simulator({}), /scaling/);
+});