This document discusses the method of least squares for fitting a linear regression model to experimental data. It explains that the least squares method finds the best-fit linear equation by minimizing the sum of the squared residuals between the measured y-values and the corresponding y-values predicted by the linear model. This best-fit linear equation can then be used for calibration or prediction purposes when analyzing an unknown sample. The key quantities derived from the least squares analysis, such as the slope, intercept, and their standard deviations, are also defined.