For all you test kit
aficionados ... I had never seen an RT-100 before. But here we are:-
OneTwoLooks like it must have been a useful piece of kit.

And
here's a nice RT-200 (in case anyone was wondering). Someone once told me (or did I dream it?) that Timeter had planned other "modules" for the RT-200 - an EST and voltmeter (as seen on the RT-100), maybe - but they never saw the light of day. Pity.
Progress? I'll let you decide.