The timing analysis is called with an executable function, and optionally a count (size, default 100) of each test set and a number of such test sets (default 10). The total number of calls will be and gives the mean runtime for the function. The standard deviation is calculated from the number of and will only be a coarse estimate. If only run with a single set the standard deviation will go away, but even if it isn't measured the execution time will still vary.