Random errors are errors made by the person carrying out the measuring, and are usually down to timing incorrectly, or reading the instrument incorrectly. It is important to try to reduce or limit the effect of random errors in measuring.
Reaction time errors and parallax errors are examples of random errors.
Parallax error is caused by a student not reading the measurement at eye level. It can lead to the reading being too high or too low.
Zero errors are caused by faulty equipment that doesn’t reset to zero properly.
Check before you start measuring that the measuring instruments read zero for zero input.
A zero error would affect every reading you take. The digital balance will be wrong by 0.02 g on every mass you measure and the force meter would be wrong by 1 N.