The word ‘statistics’ implies populations. The practical navigator uses the methods of statistics to reduce errors. However, he is concerned not with a number of craft but with one particular craft. He may therefore use statistical terms in a somewhat inexact fashion. For example, the navigator generally assumes that the distribution of errors is Guassian because he has no way of telling what it really is. In navigating a craft, the blunder rate tends to add large skirts to the Guassian distribution. In equipments, these skirts may be suppressed by limits in manufacturing tolerances.