Description: The summary: results of calculation of t- factor values for fractional degrees of freedom are considered. Values of t- factor for probabilities 0,9; 0,95; 0,9545; 0,98; 0,990,9973 are submitted for degrees of freedom from 1 up to 7 with step 0,1. The opportunity of reception of values of t- factor for degrees of freedom less then unity is shown. The formula, with high accuracy approximating relationship of t- factor on degrees of freedom is offered.
Keywords: the expanded uncertainty in measurement, coverage factor, t- factor, effective degrees of freedom