S-100 Extender Board Test Jig

[pbirkel <pbi...@mitre.org>]

I notice on the http://s100computers.com/My%20System%20Pages/6502%20Board/6502%20CPU%20Board.htm
page a bit over halfway down an interesting photo named "Letter 3 on
CRT.jpg" which shows a preliminary test of the partially-stuffed 6502
board while mounted on an S-100 extender-board serving as a test jig.

What is that board, what test/control  functions does it support, and
where might one acquire one :->?

Thanks to all and Andrew (I'm guessing ...).