The Tektronix 50M40 is a relay scanner card for the MI5010.
From Tekscope Volume 13 Number 3, September 1981 page 6:
The 50M40 Programmable Relay Scanner Card serves as a low-frequency scanner accommodating up to 16 inputs or outputs. The card contains 16 mercury-wetted relays that can be configured 16-to-1, 8-to-1, or 4-to-1 by positioning jumpers. Typical uses include control of larger relays, scanning a multimeter input over several signal points, turning on lights or audible indicators, and so forth.