5. Discussion

From these results, it was found that there is no significant difference between the resulting expanded uncertainties (at 95% confidence levels) obtained with GUM and GUM S1 (Monte-Carlo). These results are due to the linearity of the mathematical model for pH measurement. In the case of model non-linearity, there is likely to be a significant difference. For quality assurance purposes, it is advisable to run these two calculations in parallel to check the results.

In addition, the GUM and GUM S1 (Monte-Carlo) approaches lead to lower values than the global approach, because the global approach assesses uncertainties about the method (uncertainty about a single measurement is included), which implies that all sources of uncertainty are taken into account and overestimated, so the global approach takes into account the real daily variation observed in a laboratory....