Your meter might have a calibration screw and you should use that to align its readings with those of other lightmeters you use. If you use it both outdoor and indoor I would perform this alignment at no more than EV12 (1/125 f/5.6, 100 ISO) or probably less.
If you use it mainly outdoors better to make the alignment at EV14.

I would not rely on ISO fiddling for alignment as this is your backup light meter, you are going to use it rarely, and when you use it you might forget that you have to perform the ISO trick.

If the calibration procedure does not allow you to align its response to that of the other two, then I think the instrument is unreliable and better no instrument than an unreliable one.

Fabrizio