Whistle for TDC

[wxman1]

I think I read something about a device which screws into the #1 plug hole
and it makes a whistling noise as air is being forced out of the cylinder as you
turn the crank by hand. It supposedly changes pitch the instant air stops being
pushed out of the cylinder to air being sucked into the cylinder. Such as when
you pass TDC with both valves closed. It was supposed to be very accurate.

But, I can't remember where I heard about this device. Anybody ever heard about
this thing or know where you can get it?

Jim
Mt Juliet