Use the references provided. Get a cassette tape of high quality,
prerecorded, and the CD of the exact same album.

Play them both, almost in sync, you know what I mean. A five minute
song ending well within a second of each other is pretty damn
accurate. I'd actually record a few one minute bursts of 1,000 Hz or
something and leave the original information on the tape, just don't
erase it. That way it can be played in a reference deck and if the
song doesn't end on time you know the tape is stretched.

When you use the same tape and deck you lay down the 1,000 Hz you have
established the accuracy as per a prerecorded cassette. If it hasn't
been played, that is about as close as you're going to get.

About the laying down anything on that tape, like mechanically, that
stuff stretches so anything like this can only be really accurate if
the tape is actually running through a machine. Stringing out 18 ¾ "
of tape on the diningroom table isn't quite going to do the trick.

The best bet for regular decks would be to just put a sensor on the
flywheel and either put in a servo or a strobe type indicator and a
pitch control. That capstan direct is the best indicator. It could
just be a few magnets or something on the flywheel and a little coil,
or better yet optic because it's a tape deck. Either way, your
reference is quartz, so unless the tape actually slips on the capstan,
it will be about as accurate as a cassette can be.

I know what you mean about some people being hypersensitive to certain
things. If they have perfect pitch they need to make sure their toilet
is in tune. I don't mean that mean, some would just laugh themselves.
Others cannot stand wow and flutter and might even claim to hear it in
CDs. I can't stand ****ty bass. I mean if it is boomy I want out of
there, but my **** rocks the rocks. I also can't stand speakers out of
phase, can anyone else tell or what ? LOL

For a guy who is super sensitive to speed, any deck he has you should
modify. Put some reflective tapes on the flywheel(s) and a little
sensor and LED or something. Just to act as a tachometer. Eight tapes,
eight pulses. Put your motor in. Don't be whining, it has a shaft,
give it a shaft. Now electronically YOU take over that motor. Divide
down some frequency to where one eighth of the rotation of the capstan
equals 0.234375" along it's circumference.

Think of being able to excel in the industry, get respect and...... oh
****it, think of the bill you can write for this.

1. Installed new motor and servo
2. Calibrated same
3. You don't want to know the rest, but the Mossad was involved -
briefely

You gotta have a good time at this.