Least squares best-fit Line calculations have become a routine measurement tool. Unfortunately, although of great importance, the evaluation of uncertainty consistent with the Guide to the Expression of Uncertainty in Measurement (Guide) for parameters of the line, has not been routine. All too often, the estimation of uncertainty has simply involved the product of a coverage factor and the calculated standard deviation, with little consideration for the level of confidence. This paper presents simple formulas in worksheet format that enables the calculation of uncertainty for best-fit line parameters. Covered are uncertainties for the slope of the line, the data points of the line, the interpolated points, and the line as a whole. The uncertainty calculations are consistent with the (Guide), in that they have both an interval of confidence and level of confidence as in traditional Type A measurement uncertainty evaluations. In addition, examples are provided which are suitable for use as models.
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