Examine the movement in one measurement of an object that is accelerated by the power of gravity

The objective of the lab was to examine the movement in one measurement of an object that is accelerated by the power of gravity. The tools that were used are 1) Ruler. 2) An object (basketball). 3) Motion sensor. The system was to throw the ball and get something like 10 bounces altogether of in excess of one throw and get the estimation of each throw. The average gravity was 9.58 m/s^2 while the original is 9.81 m/s^2. The StDev was 0.081 which is somewhat good, but (N) was 2.97 which is greater than 2 and this means the reads where accurate, but the results are far from the original gravity which shows that there is a systematical mistake. The blunder may be on the grounds that the tallness that the ball was thrown from was not exact each throw.