Finding out the accuracy of the current probe's measurement
The sensitivity (1 mA) is the smallest current that can be consistently sensed by the instrument, i.e. it is guaranteed that you will get some reading with anything above 1 mA.

The gain accuracy tells you your measurement accuracy as a percentage of the measurement itself, so if you are sensing 1 A you can expect +-3%, typically +-1%.

The figures above are true for a properly calibrated, degaussed, warmed up and auto zeroed probe.