Random error is error that has an equal probability of being too high or too low. systematic error is error that tends toward being too high or too low.
Work Step by Step
Usually almost all measurements will have some degree of random error; however, if there are many trials, then the measurements will essentially average out. Systematic error doesn't average out through repeated experiments or trials. If there isn't a balance, then the measurements may systematically read higher than normal or lower than normal.