What are hysteresis and repeatability? 

Hysteresis and repeatability are characteristics of measurement instruments that help to define the performance of the instrument. There are several different definitions for each term. The following definitons are typical:

Repeatability: The closeness of the agreement between the results of a sample of measurements of a given parameter carried out using the same measurement procedure, using the same measuring and test equipment, under the same conditions of use and environment. Or, the ability of an instrument to return the same measurement result time after time when the measurement is made in the same way and under the same conditions.

Hysteresis: The property of a device whereby it gives different output values in relation  to its input values depending on the directional sequence in which the input values have been applied.