Voigtländer VC meter calibration

Hi! I bought recently a used tiny coldshoe lightmeter, the Voigtländer VC meter (first version). Unfortunately it seems exactly to be one stop off (overexposure). I compare with a Gossen Profisix SBC (in both reflective and incident modes) and with a Kenko KFM-1100 (= Minolta Autometer IV, incident). Basically, setting ISO 400 on the other meters gives me the same results as ISO800 on the Voigtländer.

Any way to calibrate it? Otherwise I have to adjust the ISO.

Seems like someone else had exactly the same issue: https://www.photo.net/forums/topic/527316-can-voigtlander-vc-i-meter-be-calibrated-and-how/

If it is consistently and exactly one step off I would adjust the ASA-setting accordingly and keep using it as it is.
It is a nice meter and convenient to use.

As far as I could see it was consistently 1 stop overexposure, the seller mentioned this as well when I bought it. Hoped it would just be just the way he tested (e.g. comparing with a weighted lightmeter and a bright horizon), but it confirmed here on a wall with these other lightmeters.
I will still try a bit more to verify that this is consistent over a larger range, but it seems to be. So yes, I could totally compensate with the ISO, and that's what I'll likely do. Was just hoping there is somehow a way to fix it, but it would be alright.
Or was this intended by the designer to compensate on bright horizons or since it's fine on negative film? In the old reviews I found I haven't seen this mentioned though. Or ageing of the sensor or any parts? (but I have cameras older then this which don't show ageing ligthmeters, so I guess this isn't the case, and wouldn't explain the full stop over...)