While we are at it... what made those instruments really interesting were the (in)famous prescalers. Usually ECL technology dividers by 10. In those years 5V technology (TTL, and later Schottky TTL) didn't fit the bill for 100 MHz counting...
Sad to say that there were very few of those instruments around here so the opportunities to lay hands on a surplus one are nil to me.
However I used one in my university days. From there I remember the nixies, and prior to that, from a huge calculator a friend of my uncle bought for his shoe factory accounting people.