If you type "course and speed calculator" into google, the first result is this:
http://www.adrax.com/watsons/raf.htm
which has a picture of something that says MK IIA.

DGB

Jack McAdams wrote:
My grandson gave me a beautiful Course & Speed Calculator manufactured
by W.C. Pye & Co Ltd. The mahagony box is marked as REF. No. 6B/120.
It is a MK IIA model.

It is obviously analagous to a very early E6B. My guess it is WWII
era, maybe a bit earlier.

Does anyone happen to have an instruction manual for this device? I
can probably eventually figure it out but it would be a lot easier
with the manual!

Thanks in advance for any help.