The probability that the true value of a measurement will lie within the specified uncertainty from the measured value. It must be noted that confidence levels (e.g.95%) depend on the assumed statistical distribution of the data and are calculated differently for 1 Dimensional (1D) and 2 Dimensional (2D) quantities. In the context of this standard,which assumes Normal distribution of error, the 95% confidence level for 1D quantities (e.g.depth) is defined as 1.96 x standard deviation and the 95% confidence level for 2D quantities(e.g. position) is defined as 2.45 x standard deviation.