[GreenKeys] Early teletype round keyboard.

[Jim Haynes]

The keyboard is round because of the way the thing works.  It's called a
monopulse, was intended for short range communication for such as
inter-plant.  It was called Model 36, circa 1948.

It works by sending a single pulse of variable length per character.
The leading edge of the pulse starts a typewheel rotating at the receiver
and a stop arm rotating at the transmitter, in synchronism because they
are running off the same 60 Hz power system.  The end of the pulse causes
a hammer to hit the paper tape at the receiver and print the character
that is under the wheel at the time.

It's safe to say the item is rare, if only because there was nearly zero
demand for such a product.