The error is not in reading the amps being used
The error is that the meter does not compensate for the effect heavy drain has on battery capacity
That is and added software feature programmed into more expensive dedicated Battery Meter, Instead of power meters that we 'value seekers' are buying
If you have enough battery and are using amps at near the 20 Hr rate for the bank you have , the readings will be accurate enough
But use the microwave on inverter and the affect on the battery is greater than the actual amount used
