MS2108 clamp meter, AC amps offset adjustment

[lizard]

Dear All,
  Greetings - new here.  Does anyone out there have any pointers to calibrating a Mastech 2108 clamp meter?  Specifically, I'm trying to zero out an offset in the AC current range.  For example, on power up and selecting ACA with a 3.5A current loop, the meter reads 3.8A.  On removing the loop, the reading drops to ~0.3A (consistently).  I did try with different loop currents and observed that the error is consistently close to the 0.3A offset.   Unfortunately I could find no documentation on what trimpot does what.  Any help/advice appreciated.
Thanks,
ff

[shakalnokturn]

I think getting to calibration mode involves moving a jumper inside, not sure about the cal procedure after that.
Be aware that not knowing where you're going, you could make things a lot worse. You could end up with a so badly calibrated meter that you'll have to look for a better one. (The MS2018 is the worst clamp meter I've put my nose in so far...)