It was listed as ‘PRECISION SERIES E-400 SWEEP GENERATOR F.M - TELEVISION-A.M’; which is basically gobbledegook to me, but may mean something to someone. Wikipedia has this to say:

Sophisticated tone generators will also include sweep generators (a function which varies the output frequency over a range, in order to make frequency-domain measurements)

But to be fair that's not much better! So anybody care to explain it in layman's terms?

On the other hand, I bought it because it looks so great! There's something about vintage technology ….

SteamSHIFT out.