Quote from India Four Two:
"If it was to be used to make timed heading changes, a 0-180 scale would make more sense, assuming Rate 1 turns."
Yes, quite. As I think you have in mind, on "limited-panel " (instrument flying) exercises for our commercial licences (a long time ago!), we used to time a Rate 1 turn to achieve a heading change of a certain amount. A magnetic compass, of course, goes haywire during the turn, but settles down once the wings are level again. (The gyro compass and artificial horizon had been deliberately "caged" for the exercise.)
Is it possible, as I think you are suggesting, that the instrument in question was used to time Rate 2 turns? Seems a bit unlikely, as even a Rate 1 needs (say) nearly 20 deg of bank at 120 kt. I imagine a Rate 2 would need about double that, which would be a bit tricky if accuracy were needed. And gyro compasses were pretty good by 1941...