Abstract: A test device for a thermally-activated instrument so that the accuracy of the instrument can be determined. In a first form of the invention, a cylindrical enclosure is provided for retaining the instrument and is connected to a power supply via terminals attached to the enclosure. The enclosure is slotted along its length to permit enlargement of the enclosure when necessary. A second enclosure, also slotted along its length and with a temperature sensing thermocouple attached thereto, is provided for retaining the thermally-activated instrument and is shaped to fit within the first enclosure. In a second form, a series of clustered enclosures are provided, with the enclosures being of varying sizes to accommodate thermally-activated instruments of various sizes. In a third form, enclosures are grouped into at least two separate groups, with the groups being capable of being electrically interconnected.