Repeatability refers to the variation in measurements taken by a single instrument on the same item under the same conditions. Less than perfect repeatability causes test-retest variability due to factors like intra-individual and intra-observer variability. To measure repeatability, multiple readings should be taken in the same place and calculated to find the average range to avoid errors. Calculating the mean, variance, and standard deviation of data readings can help eliminate repeatability errors by identifying measurement variability. Ensuring good repeatability through taking multiple readings is important for obtaining precise values and avoiding potential problems in measurement work.