Autometer Anolog 5" electric tach accuracy

[67ragtp]

Im sorting out a few issues with the new car. While tuning the car Ed and I relized the big analog electric tack was reading slightly over 1k maybe 1050 to 1100 while the software (hptuners), and the digital shift light with digital tach read out was reading the same 850 to 930. So it seems the tach is reading about 200rpm higher. It kind of messed with my head because I was expecting to see my idle below the 1k mark when in reality it is around 850 to 900. Is this expected accuracy? Any way to calibrate it? Any thoughts?

Thanks Rich