For instance, if one makes a 9-step Fermi estimate, at each step overestimating or underestimating the correct number by a factor of 2 (or with a standard deviation 2), then after 9 steps the standard error will have grown by a logarithmic factor of √9 = 3, so 23 = 8. Thus one will expect to be within ​1⁄8 to 8 times the correct value – within an order of magnitude, and much less than the worst case of erring by a factor of 29 = 512 (about 2.71 orders of magnitude). If one has a shorter chain or estimates more accurately, the overall estimate will be correspondingly better.