Your experiment is probably unanswerable. Find out now.
Most science projects don't fail on bad measurement. They fail because the
plan could never have answered the question. CounterLab finds the one flaw that does that,
tells you the smallest fix, and makes you write down what result would prove you wrong.
Worked example
Hypothesis. A heavier pendulum bob swings faster.
Procedure. Compare a 50 g bob on a 30 cm string against a 100 g bob on a 40 cm
string. Time one swing each.
Nothing here looks careless. It still can't work: the mass and the string length both
changed, so no stopwatch reading can tell you which one mattered.