Looks like a nice one- Since you don't have the computational part, it may well be part of a two part set for a navigator's bag. The navigator on a bomber or patrol plane or a cargo plane would not need to strap to his knee, and could use them separately. A navigator would use all the components of the one I mentioned as the navigator was responsible for guiding tha a/c, figuring fuel remaining, position, etc, where the pilot was basically the a/c driver on the big jobs. The navigator would tell him to speed up or slow down, which way to aim the nose of the plane, and let them know how long until they got home, or when they would run out of fuel if they had an engine out or fuel loss... As tou can tell, you have the wind computational section, so just follow the directions.
I will try to post pics of mine shortly: I think it is a neat looking device.