Error analysis is a common practice in science that helps to estimate the uncertainty and significance of experimental measurements, as well as the accuracy and precision of analytical methods and instruments. For instance, in physics, errors in length, mass, period, air resistance, and human reaction time must be accounted for when measuring the acceleration due to gravity. In chemistry, errors in volume, concentration, color of reagents, endpoint detection, and calibration of the equipment must be taken into account when measuring the concentration of a solution using a titration. Lastly, in biology, errors in data collection, sampling, distribution, assumptions and fit of the model must be considered when comparing the growth rates of two plant species using a linear regression model. Error propagation and error bars can be used to calculate and display the uncertainty in a final result; standard deviation and confidence intervals can be used to estimate and report the precision of a measurement; residual analysis and hypothesis testing can be used to assess and compare the validity and reliability of a model or test.