In the 'Guide to the expression of uncertainty in measurement' (GUM), guide
lines for the evaluation of the total uncertainty of an experiment are outl
ined in a manner to be adopted in all types of measurements. So far, this h
as not Very strictly been implemented in the Ion Beam Analysis (IBA) commun
ity. In this paper, the situation for a, to some extent, typical IBA measur
ement is reviewed, and factors contributing to the total uncertainty are an
alysed and discussed. Also the propagation of uncertainties is discussed. H
ow the result of a measurement should be presented, with an appropriate cov
erage factor resulting in a suitable interval for the uncertainty is also d
iscussed. An example of an uncertainty budget for an analysis of quaternary
bronzes is given as illustration. (C) 2000 Elsevier Science B.V. All right
s reserved.