Real measurements never deliver the true value of the physical quantity or measurand. The measurement uncertainty consists of a random error and a systematic error. Most of the error analysis is done for random error so that one has to be careful when treating known systematic errors. The systematic error analysis is different from the random error analysis.
Random error is produced by statistical fluctuations of the measurand 

e.g. the number of electrons passing through the current meter in each second.

Precision of the measurement device relates to low random error. Systematic error is produced by zero offset, wrong gain, changes in the environment (drift of gain and offset), imperfect observational methods, etc. It can usually be eliminated by careful calibration. But it is not always known that it exists. Accuracy of the measurement device relates to low systematic error.