If the standard deviation of an observation is ± 10-ft, the most probable error would be:
The most probable error is defined as the error for which there are equal chances of the true error being less and greater than probable error. In other words, the probability of the true error being less than the probable error is 50% and the probability of the true error being greater than the probable error is also 50%. The most probable error is given by: ± 0.6745 σ.