Means, percentages and uncertainty

Repeat measurements, leave out anomalies (values far from the rest), then take a mean.

Half the range gives a rough uncertainty.

percentage change = (final − start) ÷ start × 100

1. potato 2.50 g before, 2.30 g after
2. (2.30 − 2.50) ÷ 2.50 × 100 = −8.0%

Percentage change lets you compare pieces that started with different masses. A loss is negative.