Vacuum gauge was my first thought too; but expand the 2nd pic and look at the various scales -- 0-40-0 on the outer ring, pulling power 0-700 over half sweep on the second ring, the third ring shares 'tractive and wind resistance lb/ton' and 'acceleration % of G'.
How the h-e-double hockey sticks do you get stopping distance from a vacuum gauge? And there appears to be a needle stop at the 9 o'clock position. There's no way to select functions.
I'll be watching for one at swap meets.
