[GreenKeys] WU 1-A pics

[Jim Haynes]

They had several other similar tape readers.  I used to have one that
was a 7-something, and I have one somewhere now that has two 
electromagnets that I have never bothered to figure out what the second
one does.

W.U. tended to like magnet-operated tape readers, at least for their
office work.  They did have some motor-driven ones used in the field.

There's an interesting late one (1950s) described in Western Union
Technical Review.  It's called a loop-gate transmitter.  It reads
the tape and lets the tape form a loop above the reading head.  Then
a magnet slams the gate across so that the tape in the loop can be
read again.

This solves what is sometimes called the absorption problem.  In an
automatic switching system you need to read the destination characters
at the front of the message to decide what to do with it.  But once
you are ready to send it across the office you need to read those
destination characters again so they will be passed to the next
switching office, rather than be absorbed in the first and no longer
available.