it's a good question,
Basically, measurements are the evaluation procedures with exact (qualitative or quantitative) result,
if you take a look on the children of "Measurement of respiratory function" you will see such a concepts
Maximal voluntary ventilation measurement,
Peak expiratory flow measurement,
Lung residual volume measurement,
so all of them have numbers as a results - for example, about "1,200 mL" for a last test.
and looking on Cardiac functioning testing you'll see the descendants:
Cardiac flow study imaging
Cardiac electrophysiologic stimulation and recording study
so there are imaging, study, something that has not exact result,
that's why these concepts are the procedures.
And custom procedure data-sets usually mix-up "our" measurements and procedures (so does SNOMED also :)).
so we usually filter not by domain_id but by concept_class_id ='Procedure' working on such a custom procedure mappings.