ISO Standard 17123-4 sets out the procedure to be followed to determine and the measurement uncertainty of a distanciometer. Under this standard a simplified or complete procedure can be carried out in line with the needs of the user. As with ISO standard 17123-3, ISO standard 17123-4 seeks to ascertain the final effect caused by all the factors which contribute to determining the distance measurement uncertainty, evaluating the typical deviation of the measurement.
The expression of the combined typical uncertainty of distance can be evaluated as:
where:
= Contribution by measurement of the geometric distance using electromagnetic methods.
Manufacturers usually present the uncertainty of their equipment by means of a constant part plus a part proportional to the distance measured ± (a mm + b ppm·D), which is a way of indicating the typical deviation for any distance. If the evaluation carried out by the manufacturer is used, appropriately applying the propagation of uncertainties, the typical measurement uncertainty (σISO-EDM) obtained when measuring a given distance D, it can be evaluated by means of:
where:
a = Constant part for the distance measured.
b = Proportional part for the distance measured.
D = Distance measured.
σo,σc,σj will be the same as those used in the combined typical uncertainty of angles
TcpMDT
