While we did our projectile motion lab report for our physics class, the teacher asked: " What are errors from the experiment that caused inaccuracies in our trials? They cannot be human-caused errors like human reaction which can cause a delay in the timing process."

In our lab, we rolled a marble off a table and from that we time and measure how far the marble has traveled horizontally. So I said that air resistance is one of the errors that cause inaccuracies because when we calculated acceleration we only accounted for gravity and not air resistance. But She wants us to provide 2 more examples or errors. and I can't figure it out. So What might 2 errors from this projectile motion and acceleration due to gravity laboratory that causes inaccuracies in calculations be?