[corey_moncure]

An explanation of how the lines were synchronized between the reading and writing drums seems to be glossed over. Anyone know how they did it?

[Clamchop]

I can only guess, but, to borrow TV nomenclature, synchronizing was probably based on the horizontal blanking interval. That is, the period between lines that is most black because it's scanning the dark drum in between ends of the paper. This looks be slow enough that the operator could very well synchronize the receiver manually.

Otherwise, relying on mains frequency to control other parameters, same as TV.

The fundamental principles of this tech very much resemble TV, just with a single frame and very slowly.