[GreenKeys] ebay "Teletype Message Numbering Module"

[Jim Haynes]

Teletype (and Western Unioni and Kleinschmidt) made message number 
generating and checking machines.  In the case of this one the seller 
didn't provide a front view, which should show wheels displaying the
current message number.  These have cams to operate switches to
encode the digits as Baudot characters.  The stepping switch in
the middle sequences the characters and usually a wired-in channel
identification.  The Teletype ones were typically used in torn tape
switching equipment.

You may be familiar with an earlier technology using the Teletype MXD
3-headed tape reader, where one of the heads held a tape containing
the message numbers and channel identification.  Since it's a drag to
punch such a tape manually, without errors, and since the tapes wear
out, the mechanical numbering machine is an improvement.

Western Union back in the 1940s had a message numbering machine with
cam-operated switches.  Later they developed one using all stepping
switches.  I'm not sure why - seems like it would have been much more
costly to make that way.  This used a panel of neon lamps to display
the number.  W.U. also used similar machines to check incoming message
numbers automatically.

jhhaynes at earthlink dot net