Random errors are often unavoidable in science experiments and measurement. They are very frequently the result of human error. For example if you had to time an object falling a metre with a stopwatch, you might start or stop the watch a fraction too early or too late. The measurements are likely to be inaccurate. The amount of error in a single measurement can be reduced by taking a number of results and finding the average, but to reduce the error significantly you would have to change the method of timing. Maybe with a timer that started automatically when you let go and stopped as the object reaches the floor.
If you can spot a pattern in the measurements then you can use a graph. For example if you have to measure how much a spring stretches as you add
weights you are likely to make small mistakes in each of the measurements. However you can plot the results and draw a graph line that follows the pattern. You draw the line straight as close to the trend of points as possible but it does not have to go through all of them, some might not be accurate.
A systematic error is when the same mistake is made, in the same direction, every time. This could be a human error or it could be an error of the
instrument you are using. For example if you are weighing out some chemicals on an electronic balance you might forget to take into account the weight of the beaker each time. Another possibility is that the balance might not be set to zero and so adds or subtracts a small amount every time you use it. Systematic errors can be corrected for and by careful experiment design, they can be eliminated.