> For the complete documentation index, see [llms.txt](https://docs.aethlabs.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.aethlabs.com/microaethalometer-tm-ma450/quick-start-guide/09-calibration.md).

# Calibration

All microAeth instruments are flow calibrated at approximately standard atmospheric pressure and room temperature to ensure accurate flow rates at the time of production. Local operating conditions vary around the world. Temperature and pressure at the time of calibration are recorded in the flow calibration table header. Before instrument deployment, we suggest that the flow rates at the inlet of your microAeth instrument are checked.

In general, and especially for sampling at higher elevations, AethLabs suggests calibrating the flow of your microAeth in the location at which you plan to use it. This will ensure that the internal mass flowmeter is calibrated for the in situ atmospheric pressure. If re-calibration is needed, it is possible to calibrate to within 1-2% on average using the AethLabs MA Series Flow Calibration Kit. Only the external mass flowmeter provided in the AethLabs MA Series Flow Calibration Kit is compatible with the MA450.

![AethLabs MA Series Flow Calibration Kit (MA-FC-04)](https://272274374-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F1fOQ2MnLWcq0ntHW3LLY%2Fuploads%2Fgit-blob-3475f83d29c71fcb12574786bff1e0a0afa44e7d%2Fflow-calibration-kit-ma-fc-04.png?alt=media)

## To verify flow

The Test Flow feature checks the current internal flow reading against an external reference without performing a full calibration.

1. Connect an external low-backpressure flowmeter to the instrument inlet port (needed for comparison against an external standard).
2. Scroll through menu options to 'Test Flow' and press the center button.
3. Use the left or right buttons to select the desired target flow: 50, 75, 100, 125, 150, 175, or 200 ml/min.
4. The screen displays the current target and measured flow. Allow a few seconds for the pump speed to stabilize.
5. Compare the displayed measured flow against the external flowmeter reading.
6. Press the center button to exit.

To test in DualSpot® or SingleSpot™ mode, the sampling mode must first be set in microAeth® Manager before using the Test Flow feature.