# Record a step measurement

> Records a numeric reading against one step of a run — the pH of a medium, the mass of an ingredient, a temperature — with its unit, as the bench station running the SOP reads it from a balance, pH meter or probe.

Source: https://docs.xplantpro.com/docs/api/sops/create-sop-step-measurement

`POST https://app.xplantpro.com/api/v1/sop-runs/{id}/steps/{stepId}/measurements`

- Required scope: `write:sop_steps`
- Credentials: workspace API key (`xpk_`)
- Idempotency-Key: honoured (24 hours)

The reading joins the same trail as the step events, with `eventType` `measured`, so a run reads in one order. The unit is required: a number without one is not a record anyone can rely on later. Send an `Idempotency-Key` so a retried post does not record the reading twice.

Send an `Idempotency-Key` header to make retries safe: a repeat with the same key within 24 hours returns the first response instead of writing twice. See [Idempotency](https://docs.xplantpro.com/docs/idempotency.md).

## Path parameters

| Name | Type | Required | Description |
| --- | --- | --- | --- |
| `id` | string (uuid) | Yes | The run's id. |
| `stepId` | string | Yes | The `id` of one of the steps in the version the run follows — the version in force when the run started, whose steps Get an SOP lists in `version.steps` while it is still in force. Any other `stepId` is refused and nothing is recorded. |

## Headers

| Name | Type | Required | Description |
| --- | --- | --- | --- |
| `Idempotency-Key` | string | No | Any unique string you choose per logical write. A retry carrying the same key within 24 hours returns the first result instead of writing again. Scoped to your API key and this operation. 8–255 characters. Must match `^[A-Za-z0-9._:~-]+$`. |

## Request body

| Field | Type | Required | Description |
| --- | --- | --- | --- |
| `metric` | string | Yes | What was measured, in your own words — `temperature`, `ph`, `mass`. 1–60 characters. |
| `value` | number | Yes | The reading. |
| `unit` | string | Yes | The unit the reading is in, such as `C`, `pH` or `g`. Required. 1–20 characters. |
| `recorded_at` | string (date-time) | No | When it happened, as an ISO 8601 timestamp in UTC (`2026-09-25T08:30:00Z`) or with an offset (`2026-09-25T10:30:00+02:00`). Defaults to when xPlant receives it. |
| `notes` | string | No | Anything the reading needs beside it. Up to 500 characters. |

## Example

**curl**

```bash
curl -X POST https://app.xplantpro.com/api/v1/sop-runs/2a4c6e8b-1d3f-4b5a-a7c9-e1f3a5b7c9d1/steps/step-3/measurements \
  -H "Authorization: Bearer $XPLANT_API_KEY" \
  -H "Idempotency-Key: station-3-wk38-step3-ph" \
  -H "Content-Type: application/json" \
  -d '{
    "metric": "ph",
    "value": 5.7,
    "unit": "pH",
    "recorded_at": "2026-09-25T08:21:40Z",
    "notes": "Initiation medium before pouring."
  }'
```

**JavaScript**

```js
import { XPlantClient } from "@shmaplex/xplant-sdk";

const client = new XPlantClient({ apiKey: process.env.XPLANT_API_KEY });

const measurement = await client.sopRuns.recordMeasurement(
  "2a4c6e8b-1d3f-4b5a-a7c9-e1f3a5b7c9d1",
  "step-3",
  {
    metric: "ph",
    value: 5.7,
    unit: "pH",
    recorded_at: "2026-09-25T08:21:40Z",
    notes: "Initiation medium before pouring.",
  },
  { idempotencyKey: "station-3-wk38-step3-ph" },
);
```

**Python**

```python
import os
import requests

resp = requests.post(
    "https://app.xplantpro.com/api/v1/sop-runs/2a4c6e8b-1d3f-4b5a-a7c9-e1f3a5b7c9d1/steps/step-3/measurements",
    headers={
        "Authorization": f"Bearer {os.environ['XPLANT_API_KEY']}",
        "Idempotency-Key": "station-3-wk38-step3-ph",
    },
    json={
        "metric": "ph",
        "value": 5.7,
        "unit": "pH",
        "recorded_at": "2026-09-25T08:21:40Z",
        "notes": "Initiation medium before pouring.",
    },
    timeout=10,
)
body = resp.json()
if not body["ok"]:
    raise RuntimeError(f"{resp.status_code} {body['code']}: {body['error']}")
measurement = body["data"]
```

## Response

`201` with `{ "ok": true, "data": … }`. `data` holds the result.

| Field | Type | Required | Description |
| --- | --- | --- | --- |
| `id` | string (uuid) | Yes | — |
| `runId` | string (uuid) | Yes | The run the evidence belongs to. |
| `stepKey` | string | Yes | The step it was recorded against — the `stepId` it was posted to. |
| `eventType` | string | Yes | `confirmed`, `scanned`, `skipped`, `note` or `device_state` for a step event; `measured` for a measurement. |
| `recordedAt` | string | Yes | When it happened: the `recorded_at` that was sent, or when xPlant received it. |
| `payload` | object | Yes | The detail sent with the event. For a measurement: `metric`, `value`, `unit`, and `notes` when there were any. |

```json title="Response"
{
  "ok": true,
  "data": {
    "id": "b2c3d4e5-f6a7-4b8c-9d0e-1f2a3b4c5d6e",
    "runId": "9a8b7c6d-5e4f-4a3b-9c2d-1e0f9a8b7c6d",
    "stepKey": "step-2",
    "eventType": "measured",
    "recordedAt": "2026-09-25T08:21:40+00:00",
    "payload": {
      "metric": "ph",
      "value": 5.7,
      "unit": "pH",
      "notes": "Initiation medium before pouring."
    }
  }
}
```

| Response header | Meaning |
| --- | --- |
| `Idempotent-Replay` | `true` when this response is a replay of an earlier request with the same `Idempotency-Key`. |
| `X-Request-Id` | Identifies this request. Include it when you contact support. |

## Errors

| Status | Code | When |
| --- | --- | --- |
| `400` | `VALIDATION_ERROR` | The request body is not valid JSON. |
| `401` | `UNAUTHORIZED` | The key is missing, malformed or revoked, or its owner is no longer a member of the workspace. |
| `402` | `PAID_PLAN_REQUIRED` | The workspace's plan does not include the API. The full API is included with xPlant+ Teams and Enterprise; on Hobby and Pro Lab, keys can connect devices only. |
| `403` | `FORBIDDEN` | The key lacks a scope this operation requires, or its owner's current role in the workspace cannot use it — a key never does more than its owner can in xPlant. `error` names the scope, and for a role, the role it needs. |
| `403` | `DEVICE_TOKEN_NOT_ACCEPTED` | A device token was sent; this operation needs a workspace API key. |
| `404` | `NOT_FOUND` | No run with this id exists in the key's workspace, or the run id is not a well-formed id. |
| `404` | `NOT_FOUND` | `stepId` is not the `id` of a step in the version the run follows, or the run follows no recorded version of its SOP and so has no steps to record against. Nothing is recorded. |
| `409` | `IDEMPOTENCY_IN_FLIGHT` | A request with this `Idempotency-Key` is still being processed; retry after `Retry-After` seconds. |
| `409` | `SOP_RUN_CLOSED` | The run has ended: its status is one of `completed`, `failed`, `cancelled`, `archived`. An ended run's record is final and takes no more evidence. |
| `422` | `VALIDATION_ERROR` | The `Idempotency-Key` header is malformed. |
| `422` | `VALIDATION_ERROR` | A field failed validation — a missing `unit`, a `value` that is not a number, or a `recorded_at` that is not a timestamp with a time zone. `error` gives the first problem but does not name the field. |
| `429` | `RATE_LIMIT_EXCEEDED` | Too many requests for this key, device token or workspace. Wait `Retry-After` seconds. |
| `500` | `SOP_STEP_EVENT_CREATE_FAILED` | The evidence could not be saved. Retry with the same `Idempotency-Key`. |

Branch on `code`, never on the `error` text. See [Errors](https://docs.xplantpro.com/docs/errors.md).