I woke up this morning with a smile because I realized that I can
extend the rotating head thread!  Years ago there was an article in
AMICA magazine about how Dr. Hickman's piano hammer speed spark
measuring device worked.  As I recall he used a rotating drum with
a spirally wound ground wire with paper moving over it.  The effect
was to stretch out the distance on the paper between the two sparks
from one hammer on it's rapid way to the strings.

I probably don't have it just right, but I do remember thinking
that this was the same principle of the rotating head VCR.  Now:
Did Dr.  Hickman invent the actual rotating chronometer, or was it
already a scientific measuring tool?

Allan Merralls