A map of the GUM family: which uncertainty document answers which question

'The GUM' is shorthand for a whole family of JCGM documents, and knowing which member answers which question saves real time.

JCGM 100:2008 is the core Guide to the Expression of Uncertainty in Measurement: Type A and Type B evaluation, the law of propagation of uncertainty, expanded uncertainty and coverage factors. JCGM 101:2008 (Supplement 1) is the Monte Carlo method — propagate whole probability distributions when the model is non-linear or the distributions are ugly. JCGM 102:2011 (Supplement 2) extends that to models with multiple output quantities and their correlations. JCGM 104 is the readable introduction most newcomers should actually start with. JCGM 106:2012 handles conformity assessment — false accept and false reject risk, acceptance intervals and guard bands. And JCGM GUM-6:2020 addresses the step every other document takes for granted: developing the measurement model in the first place.

The family has its history: a heavily revised core GUM circulated in draft in the mid-2010s and met substantial resistance from the community — enough that the committee stepped back and pursued the incremental path instead. Whatever future editions bring, all of these documents are freely downloadable from the BIPM, and the Atlas standards index links each one.