What do the digits of precision of the DRO mean?

Many mill DROs, or digital readouts, show four numbers to the right of the decimal point, or measurements to the ten-thousandths of an inch (0.0001”) (with there being fewer digits of precision if the DRO is reading millimeters). While this number appears on the DRO, it is not to be trusted! The sensors on the mill are not precise enough to accurately measure to this resolution, and the number in this place will be either a 0 or a 5.