Life wasn’t easy in phototype days

While I more or less have a notion of how metal type and measurement works, I’m at a loss reading through specimen and instructions from film-setting days. Yes, I know there have been A, B, C and sometimes D masters to cover different ranges of size (instead of having only one scaled to all sizes), but this sounds complicated:

Specimen for Helvetica Compressed by Mergenthaler Linotype


Monotype Newsletter 92 on the occasion of Helvetica being licensed for Monotype’s hot-metal and photo composition machines, 1972