The terms precision and accuracy are used in connection with the performance of the instrument.
Precision is the repeatability of the measuring process. It refers to the group of measurements for the same characteristics taken under identical conditions.
It indicates to what extent the identically performed measurements agree with each other. If the instrument is not precise it will give different (widely varying) results for the same dimension when measured again and again.
The set of observations will scatter about the mean.
The scatter of these measurements is designated as 5, the standard deviation. It is used as an index of precision.
The less the scattering more precise is the instrument. Thus, lower, the value of 5, the more precise is the instrument.