#ds_error value mm value ppm
This defines the default error that applies to subsequent distance data (slope or horizontal distances). The error is defined by a millimetre component and a part per million component. The total error is calculated from the square root of the sum of the squares of these components. For example if a the error was defined as "3 mm 2 ppm", then the error on a 2000m line would be 5 mm.