If there was a scale fixed to the circle-watch of the AT-1, one could easily "place" luminosities like on the Zero.adjust dial of the Profisx meter.
So there only are for sure 1/2 and 1 stop deviation. 1 1/2 and 2 stops would also be possible by extrapolation in case of linearaity.
The meter of the AT-1 is 2 stops less sensitive than that of the AE-1. It also uses a photo-resistor instead of a photo-diode/trabsistor.