A test sample support assembly having its greatest utility in a length measuring device in a temperature controlled environment. The sample support assembly has a main support, a pair of insulating members and a sample support. In one embodiment of this invention the sample support is made of a substantially distortion-free material thereby precisely positioning the sample within the temperature controlled environment. In the other embodiment of this invention the sample support acts as the temperature controlling element. The sample support is adjustably mounted with respect to the main support. This adjustable feature permits corrective movement of the sample support to take place in order to compensate for the undesirable movement of the sample support.