Looks at this beauty! It is a Hewlett-Packard Wide Range Oscillator model 200CD. It emits a tone like a sign wave generator. It is a sweepable tone. The large dial makes it somewhat easy to find notes so you can play this like a chromatic instrument. The big dial also has a smaller fine tune dial. I have begun to label the places where you find whole notes to make it that much easier to play along with other instruments. I opened it up when I got it to fix the dial and found (among the standard issue mouse turds) hand written schematics made by someone in Mazzola, Montana. Weird. I got this FREE from my friend Tim… It was spring cleaning at his house and I scored a couple of nice ‘gimme’s’ that day. He also gave me his very first guitar. It had all of its frets removed (on purpose? by accident?) and came with a Bigsby B-bender bridge. Hot! I hope to make this beast live again in one form or another one day. Thanks Tim!