Datron 4200 options?

[Scopetechniques]

Hello,

I have a Datron 4200 AC Calibrator with options 30, 42, 80, 90.
It is on the original label from Datron attached to the back of the unit "30 42 80 90".
I am having a problem identifying option 42.

30 - AC Current calibrator
41 - Rear output (I thought the 42 was a typo on my unit, but it does not have rear output and never did).
42 - ?
80 - 115VAC 60Hz
81 - 115VAC 50Hz
82 - 115VAC 400Hz
90 - Rack mount kit installed.

Thanks,
Victor