=+70. The article “Error Distribution in Navigation” (J. Institute of Navigation, 1971: 429–442) suggests that

the frequency distribution of positive errors (magnitudes of errors) is well approximated by an exponential distribution. Let x denote the lateral position error (nautical miles), which can be either positive or negative, and suppose the density function of x is f(x) 5 (.1)e 2.2|x|

for 2∞ , x , ∞.