Found it! Aisha (below) is absolutely correct. Here's one of these in a collection, with both sides available to see:
http://collections.si.edu/search/results.htm?q=Univac+computer

I've heard, not about this simple calculator, but about some of the games hackers could play with drum memory, by, for example, deliberately using WORST latency rather than best.

Sadly, none of the descriptions of Minimum Latency Programming that I could find gave me enough information to *quite* see how the calculator should be used.