[ARC5] OT - the BC-221-D, tube types.

[Jim Haynes]

As a matter of interest, someone a few years back asked me to look up
an article in Electronics magazine about how the BC-221 calibration
books were made in production.  I don't remember all the details, but
there was a fixture that would motor drive the knobs on a whole row
of the BC-221s.  And each time the frequency crossed some calibration
frequency a tick mark was made.  Then they used a machine that was used
in banking to calculate and print loan payment books, and it would do
the interpolation between calibration points and print the books.