calibrating chinese style

I got this cheap Ebay junk installed and working but I need help calibrating same. I tried to calibrate on the bench first, but it didn't like being calibrated with low current. Now, I'm sorry that I ****** up the factory calibration. Virtually no documentation came with this POS. I did find some info from internet searches saying calibrate current first, then voltage. OK. My attempted bench calibration would set the current, then when I bring the voltage in, the current was off. Bring the current in, the voltage was off. Back and forth, back and forth. The POS was lucky I didn't hammer it right then and there. As you can see in the pic, there are two trims, one for volts, one for amps. Anybody can Help?

The stunt? Per the instructions, the stunt is wired in series with the load on the negative side. I isolated the body current from the starter current by removing the engine to body bond, so that the starter current does not pass through the shunt. The meter is working, just need calibration. I did the big3 on this vehicle, plus 4gauge to starter and main fuse distribution box. (very needed improvement) I verified that the engine/transmission bond is isolated from the body.

is that from Asia Engineer? I just bought some temp gauges from them and they're damn nice.

Are you saying the meter has two display modes, one for current and one for current? Or is the meter only supposed to measure volts, with the current shunt supplied to convert the current to voltage for the meter? Calibration usually involves two adjustments, one for zero volt offset, and another for gain at full scale input. I don't know what kind of setup would have a pot adjustment for current and another for voltage. I see two pots, but can't see anything marked current or voltage from the picture. You received instructions with the meter that said that was the purpose of the pots? Or does virtually no documentation mean you didn't get anything with it?