diff --git a/src/components/config/CalibrationModal.tsx b/src/components/config/CalibrationModal.tsx
index 4a8a0ba..f23c1fc 100644
--- a/src/components/config/CalibrationModal.tsx
+++ b/src/components/config/CalibrationModal.tsx
@@ -4,7 +4,8 @@ import { useCallback, useEffect, useRef, useState } from "react";
 import { Box, Flex, Input, Table, Text } from "@chakra-ui/react";
 import { Card, Chip, Icon, Mono } from "@/components/primitives";
 import { useNovaStore, sel } from "@/lib/store";
-import type { SensorEntry } from "@/lib/types";
+import { isRobustMethod, repeatedMedianFit, theilSenFit } from "@/lib/analysis/calibrate";
+import type { ConvertMethod, SensorEntry } from "@/lib/types";
 import { TABLE_CSS, IconButton } from "./fields";
 
 const CAPTURE_MS = 10_000;
@@ -34,6 +35,14 @@ function linearFit(pairs: Pair[]): { m: number; b: number } | null {
   return { m, b };
 }
 
+/** The line the backend will apply for this sensor's conversion method. */
+function fitFor(method: ConvertMethod | undefined, pairs: Pair[]): { m: number; b: number } | null {
+  if (!isRobustMethod(method)) return linearFit(pairs);
+  const fit = method === "theil_sen" ? theilSenFit : repeatedMedianFit;
+  const line = fit(pairs.map((p) => p[0]), pairs.map((p) => p[1]));
+  return line && { m: line.slope, b: line.intercept };
+}
+
 export interface CalibrationModalProps {
   sensor: SensorEntry;
   onSave: (calibration: Pair[]) => void;
@@ -119,7 +128,7 @@ export function CalibrationModal({ sensor, onSave, onClose }: CalibrationModalPr
   // Δ = valueNow / m. Requires a trend (≥2 points), a non-flat slope, and a
   // live value.
   const liveValue = live?.value ?? null;
-  const fit = linearFit(pairs);
+  const fit = fitFor(sensor.convert?.method, pairs);
   const canZero = liveValue != null && fit != null && fit.m !== 0;
 
   function zeroAtCurrent() {
diff --git a/src/components/config/SensorsTable.tsx b/src/components/config/SensorsTable.tsx
index 6db494e..89ec9e3 100644
--- a/src/components/config/SensorsTable.tsx
+++ b/src/components/config/SensorsTable.tsx
@@ -17,7 +17,14 @@ import { CalibrationModal } from "./CalibrationModal";
 
 const SENSOR_TYPES: SensorType[] = ["PT", "LC", "TC"];
 const SOURCES = ["GCS", "TCS", "FAS"] as const;
-const CONVERT_METHODS: ConvertMethod[] = ["none", "zero_offset", "linear", "polynomial"];
+const CONVERT_METHODS: ConvertMethod[] = [
+  "none",
+  "zero_offset",
+  "linear",
+  "polynomial",
+  "theil_sen",
+  "repeated_median",
+];
 
 export interface SensorsTableProps {
   sensors: SensorEntry[];
diff --git a/src/lib/analysis/calibrate.ts b/src/lib/analysis/calibrate.ts
index 72e8952..cfa8966 100644
--- a/src/lib/analysis/calibrate.ts
+++ b/src/lib/analysis/calibrate.ts
@@ -7,16 +7,75 @@
  * linear interpolation between breakpoints; outside it, the end segment's slope
  * is extended rather than clamped, so an over-range reading stays visibly
  * over-range instead of flat-topping at the last calibrated point.
+ *
+ * The `theil_sen` and `repeated_median` methods instead fit one robust
+ * straight line through all the points, matching the backend's
+ * `data_service.py`, so a single bad point doesn't bend the result. The line
+ * also carries on past the outermost points.
  */
 
-import type { ConvertSpec, SensorBinding, SensorEntry } from "@/lib/types";
+import type { ConvertMethod, ConvertSpec, SensorBinding, SensorEntry } from "@/lib/types";
 import type { ChannelBinding } from "./types";
 
+/** `value = slope * raw + intercept`. */
+export interface CalibrationLine {
+  slope: number;
+  intercept: number;
+}
+
 export interface CalibrationTable {
   /** Raw breakpoints, sorted ascending and de-duplicated. */
   xs: Float64Array;
   /** Engineering values at each breakpoint. */
   ys: Float64Array;
+  /**
+   * Set only for a robust method: the fitted line, used instead of the
+   * breakpoints. `null` when the points give no slope (fewer than two
+   * different raw values), and the raw value then passes through, as in the
+   * backend.
+   */
+  line?: CalibrationLine | null;
+}
+
+export type RobustMethod = "theil_sen" | "repeated_median";
+
+export function isRobustMethod(method: ConvertMethod | undefined): method is RobustMethod {
+  return method === "theil_sen" || method === "repeated_median";
+}
+
+function median(values: number[]): number {
+  const s = [...values].sort((a, b) => a - b);
+  const mid = s.length >> 1;
+  return s.length % 2 ? s[mid] : (s[mid - 1] + s[mid]) / 2;
+}
+
+/** Slopes from point i to every other point with a different raw value. */
+function slopesFrom(i: number, xs: number[], ys: number[], onlyAfter: boolean): number[] {
+  const out: number[] = [];
+  for (let j = onlyAfter ? i + 1 : 0; j < xs.length; j++) {
+    if (j === i || xs[j] === xs[i]) continue;
+    out.push((ys[j] - ys[i]) / (xs[j] - xs[i]));
+  }
+  return out;
+}
+
+function lineWithSlope(slope: number, xs: number[], ys: number[]): CalibrationLine {
+  return { slope, intercept: median(xs.map((x, i) => ys[i] - slope * x)) };
+}
+
+/** Theil–Sen: slope is the median of the slopes between every pair of points. Ignores up to ~29% bad points. */
+export function theilSenFit(xs: number[], ys: number[]): CalibrationLine | null {
+  const slopes = xs.flatMap((_, i) => slopesFrom(i, xs, ys, true));
+  return slopes.length ? lineWithSlope(median(slopes), xs, ys) : null;
+}
+
+/** Siegel's repeated median: each point's median slope to the others, then the median of those. Ignores up to half the points being bad. */
+export function repeatedMedianFit(xs: number[], ys: number[]): CalibrationLine | null {
+  const perPoint = xs
+    .map((_, i) => slopesFrom(i, xs, ys, false))
+    .filter((s) => s.length > 0)
+    .map(median);
+  return perPoint.length ? lineWithSlope(median(perPoint), xs, ys) : null;
 }
 
 export class CalibrationError extends Error {}
@@ -64,11 +123,19 @@ export function validateCalibrationTable(
  */
 export function applyCalibration(
   raw: Float64Array,
-  { xs, ys }: CalibrationTable,
+  { xs, ys, line }: CalibrationTable,
 ): Float64Array {
   const n = xs.length;
   const out = new Float64Array(raw.length);
 
+  if (line !== undefined) {
+    for (let i = 0; i < raw.length; i++) {
+      const v = raw[i];
+      out[i] = !Number.isFinite(v) ? NaN : line ? line.slope * v + line.intercept : v;
+    }
+    return out;
+  }
+
   if (n === 0) return out.fill(NaN);
   if (n === 1) {
     for (let i = 0; i < raw.length; i++) {
@@ -140,7 +207,14 @@ export function calibrationFor(convert: ConvertSpec | undefined): CalibrationTab
   const table = convert?.calibration;
   if (!table || table.length === 0) return null;
   if (convert?.method === "none") return null;
-  return validateCalibrationTable(table);
+  const validated = validateCalibrationTable(table);
+  if (!isRobustMethod(convert?.method)) return validated;
+
+  // Fit every point, duplicated raw values included, as the backend does.
+  const xs = table.map((p) => Number(p[0]));
+  const ys = table.map((p) => Number(p[1]));
+  const fit = convert.method === "theil_sen" ? theilSenFit : repeatedMedianFit;
+  return { ...validated, line: fit(xs, ys) };
 }
 
 /** True when the sensor declares a usable calibration table. */
diff --git a/src/lib/analysis/index.ts b/src/lib/analysis/index.ts
index f71b3e7..9ee4e3e 100644
--- a/src/lib/analysis/index.ts
+++ b/src/lib/analysis/index.ts
@@ -19,9 +19,12 @@ export {
   bindingColumnKey,
   calibrationFor,
   hasCalibration,
+  isRobustMethod,
+  repeatedMedianFit,
+  theilSenFit,
   validateCalibrationTable,
 } from "./calibrate";
-export type { CalibrationTable } from "./calibrate";
+export type { CalibrationLine, CalibrationTable, RobustMethod } from "./calibrate";
 export {
   buildChannelOwners,
   deriveActuationEvents,
diff --git a/src/lib/analysis/pipeline.ts b/src/lib/analysis/pipeline.ts
index c19c2f9..a0e7bef 100644
--- a/src/lib/analysis/pipeline.ts
+++ b/src/lib/analysis/pipeline.ts
@@ -171,7 +171,11 @@ export function buildDataset({
     if (calibration) {
       values = applyCalibration(col.values, calibration);
       origin = "calibrated";
-      applied.push(`calibration (${calibration.xs.length} pts)`);
+      applied.push(
+        calibration.line !== undefined
+          ? `calibration (${sensor.convert?.method}, ${sensor.convert?.calibration?.length ?? 0} pts)`
+          : `calibration (${calibration.xs.length} pts)`,
+      );
     } else {
       values = Float64Array.from(col.values);
       origin = "raw";
diff --git a/src/lib/types.ts b/src/lib/types.ts
index 4605146..944854b 100644
--- a/src/lib/types.ts
+++ b/src/lib/types.ts
@@ -19,7 +19,13 @@ export type ActuatorType =
   | "powered_gpio_device"
   | "gpio_device"
   | "motor";
-export type ConvertMethod = "none" | "zero_offset" | "linear" | "polynomial";
+export type ConvertMethod =
+  | "none"
+  | "zero_offset"
+  | "linear"
+  | "polynomial"
+  | "theil_sen"
+  | "repeated_median";
 export type ClientRole = "viewer" | "pad" | "operator" | "admin";
 
 export type SensorBinding =