Hello weldhawk71, your machines may not be as far off as you think. I say it that way because to truly "test" the calibration of a machine you will need a load bank with meters that has been calibrated. Even though you are using a calibrated meter there are other variables that enter into the process that won't allow a great amount of consistency using your current method. I will try to attach a couple of items to explain this further. Best regards, Allan

Keep all the electrical connections clean and corrosion free.  Sensors for digital readouts can be voltage sensitive as well and a surge from having to boost a battery or short and they will never be the same have to replace them new.  Most of the readouts are adjustable but many times need the manufacturers instructions to adjust them or have to send back to them.  Had all the battery electrical anlyzer testers I want with digital guages they never stay accurate on something like that and I was just filling the pockets of the Snap On man so went back to a older Sun tester can get parts for with analog guages and no more problems now :)  Digital may look cool but sometimes it falls back on the old KISS theory !

where are you clamping the meter? Do you have a Simpson analog volt/ohm meter? You will get a better reading from it than a digital. Lincoln and Miller allow for a 10 % + or - variance.