The MOSAID SRT1 is a RAM Tester plug-in for the TM500 system.
The SRT-1 (Simple Ram Tester) consists of two double-width plugins which are commonly encountered in a TM504 mainframe. It is very probable that additional interconnections, which are not routed via the TM500-backplane, between the modules are used.
The left side unit is labeled as "Main Module" and contains adressing/sequencing controls and paired x/y gain and shift setting knobs (for a x/y monitor?).
The right side unit is labeled "Byte Wide Memory Module" (in all 2 configurations seen until today) and contains analogue preset pots, a 4-digit display and additional controls as well as the interface to the external frontend box.
Mosaid Systems Inc. appears to be a defunct company formerly located in Canada.