Chronographs, used to measure bullet speed, commonly calculate Muzzle Velocity or MV of each shot; and the Average, Extreme Spread or ES, and Standard Deviation or SD of a set of shots.
We test a sample to estimate values of the population, of values of a zillion shots.
We sometimes see unusual numbers while chronographing, with MV being very high or low for some shot/s compared with the other shots in the set.
We can examine a test by dividing ES / SD and checking the table.
Sets of n shots will have ES / SD less than the table values 97% of the time. So, we are 97% sure that a set of shots, with ES / SD GREATER than the table value, does NOT have Average, ES and SD that are representative of the population.
If a set of n = 10 shots has ES / SD greater than 4.67; then we are 97% sure that something is amiss. Increasing the number of shots, n, may bring ES / SD down.