the.com/standard deviation
the average amount your data lies before it tells you the truth.
means a number measuring how spread out values are from their mean, low means clustered tight, high means chaos.
from coined by statistician karl pearson in 1893, though the underlying math traces to gauss and the theory of errors in early astronomy.
symbollowercase sigma, greek letter, math royalty
calculationsquare root of the variance, basically
bell curve rule68 percent of data falls within one
zero meaningzero deviation means everything is identical