Variance is a measure of statistical dispersion about the mean. The larger the variance, the further individual values of the random variable (observations) tend to be from the mean, or average. Variance exists between individuals of a species for a multitude of traits, including dentition. A number of different genetic, environmental, and mechanical factors may be at the root of this variance. Even in cases of monozygotic twins, dental variation is seen in their individual dentition. This may be due to epigenetic factors, environmental variances, and different phylogenetic influences. Variance in dentistry can also be found in the measurements taken by different tools. Each tool used is calibrated per industry standards but subtle differences in each individual tool will result in minor, or sometimes major, variances. Careful calibration prior to use, proper tool cleaning and maintenance, and proper tool storage and care will help diminish the likelihood of extreme variance between tools.