In adding to the calibration issue. It would seem that the calibrating itself would in most cases depend on some human input.
The device I have is the ADS Determinator. I must also add that in most cases the plus reading was at .0054 or .0055.
I did have one or two readings at a .0060 and one as low as 0040. But in any case for the most part they were at a
.0055. Also when mine is calibrated its done in a place that is off limits to the customer.