I used that with a neon "night light" before I bought a proper
tachometer. I used a highlighter to colour the band of prime interest
for greater ease in locating it in the dim lighting.
Yeah, I still don't own a tach, other than one of those non-contacting
electrostatic pickup ones used for checking the speed of one cylinder
But, when I was curious about what the actual spindle speeds on my old
Stark lathe were after I'd bought it and fitted it up with a step V-belt
pully and a Craftsman speed change pully rig made for use with wood
lathes, I did this:
I securely taped a small magnet on the inside of one of the chuck jaws,
hooked an old relay coil across the input of my oscilloscope, held the
coil near the spinning chuck, measured the pulse spacing with the
scope's time base, and did the math.
Pretty is as pretty does.....
PS- Here's my Stark lathe:
That rectangular tag hanging off a hook to the left of the chuck is a
gage I made equal to the didtance between the top of the cross slide and
the spindle centerline. I makes for easy setting of a tool bit in the