[GreenKeys] Re: Operations per minute...

[Don Robert House]

That is what is neat about the Model 37 and a few older Teletype  
models that set up a character in one-half revolution of the shaft.
So the operations per minute would surprise people.

Don


On 15 Nov 2008, at 11:47 AM, WA5CAB at cs.com wrote:

Lar,

As someone else already said in part, the 5-unit or 5-level  
asynchronous Baudot teleprinter code has five information bits, a  
start bit and a stop bit.  In most Model 14/15/19/20/26/28 machines,  
the stop bit is longer than the other six.  For nominal 60 wpm  
machines the stop bit is 31 ms.  The others are 22 ms.  So the length  
of one character is 163 ms.  If the average word is taken to be five  
letters long plus one space, the average word is 978 ms long.  There  
is a little overhead in the CR and LF after each line of printing so  
that after several lines the average word time grows to nearly one per  
second or 1000 ms.  And one word per second is 60 words per minute.

The published or stated baud (bit per second) rates ignore the length  
of the longer stop bits and are simply the inverse of the bit length.   
22 ms inverted is 45.4545...

If you run the same calculations against all four common speeds, you  
will see that it takes slightly different assumptions and fudge  
factors to get the nice neat numbers.  I assume that the engineers  
involved realized that fractional wpm figures would only confuse  
senior management and rounded everything off (or more likely up) to  
neat short figures.  The published baud rates, however, are accurate,  
at least if you take them out to enough decimal places.

Another figure of merit that seems to have fallen into disuse but used  
to be commonly stated instead of baud rate is Operations Per Minute  
(opm).  60 speed machines run at 368 opm.

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