[GreenKeys] Model 28 TD - use of dual shaft (LBXD) vs single shaft (LXD)

[Jim Haynes]

Was it the LAXD that had two shafts and a crawling head reader?  That
could be used on an ASR set so the reader could read the last
character punched, in addition to all the other tricks possible
with a two-shaft reader.

Goes back to the FRXD which combined a Model 14 reperf with a
crawling head reader (two shaft) for use as a storage buffer in
switching systems.  Then the Model28 line included RT stands,
which were some kind of punch and some kind of reader for storage
and speed conversion in switching systems.  ADIS used a high/low
speed converter with BRPE punch and LBXD reader, and a low/high
converter with LPR punch and BX high speed reader.  These RT stands
accomodated large tape supply and takeup reels and were narrow
enoough that two could fit side by side in a rack cabinet.  And
finally there was an LRXD which replaced the FRXD and had the
same size base as the FRXD.  These were used to convert older
switching systems (81D1) to be able to operate at 100 wpm.
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