Question about calibration offset

I've turned off auto-calibration for my Vector 3 and I always calibrate them manually before each ride with my FR-935. I configured the option to have a calibration prompt each time the V3 connects to the 935 and I simply click yes and I calibrate, very simple and completely under control.

The strange things is that sometime after the calibration I get a message "Offset 0" and sometime I get a different message with the current reading of the torque measured (a variable number near 0). I think that in both cases the calibration should be successfull but I can't understand what this different behaviour depends on ...

The Other thing I've seen is that when I frstly installed my V3 the calibration offset after calibration was often different from 0 (even 40 or 60), but now it's always 0.

Is this a common behaviour? Any idea about the different calibration outputs? From what I've understood in the manuals, the calibration torque value should be displayed if you do a second calibration just after the first one, but I'm not sure that this is correct