[GreenKeys] 7.42 vs. 7.0 machines/

[Jim Haynes]

In a recent posting I told the origin of 7.42, it being a design sort-of
flaw in a Western Electric printing telegraph.  Morkrum could do 7.00 code
from the beginning, but the Bell System required 7.42 for interoperability
with the earlier W.E. machines.

Western Union always liked 7.00 code and bought most of their machines
that way.  Bell System and the U.S. military and other non-W.U. customers
got 7.42 from Teletype.

Teletype printers can receive 7.00 code just fine, at full speed as it
comes from a tape transmitter.  That's because in Teletype design the
receiving shaft completes its rotation in time to latch up the clutch
even if the stop pulse is only one unit long.  With 7.42 it just rests
a little longer.  I believe this is true even for the Model 32, but
don't hold me to that.  I don't know that much about the 32/33 line.

A 7.00 keyboard requires a different cam and gearing from the 7.42
because the keyboard shaft has to turn faster in 7.00.