Measurement of coolant freezing point
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We have and an Extech R41 model refractometer in the MagAO-X "Cooling system parts, tools, and hardware" box in the cleanroom.
It is in a black semi-hardshell case about the size of an eyeglasses case.

Usage
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.. image:: figures/ExtechR41_refractometer_UserManual.png

Latest measurements
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On 2026-03-21 we measured the MagAO-X instrument glycol concentration using the refractometer and found a freezing point of about -22 Celsius.

.. image:: figures/ethylene_glycol_refractometer_20260321.jpeg