Avaliable measurements may be accessed by their name, McMeasure.Attributes(mcmaidName). Or they may be accessed by their ID, McMeasure.Attributes(mcmaidID). Measurements may either be built in ones, or may be ones registered by a call to McEngine.RegisterUserMeasurement.
The accessed measurement will be automatically added to the collection, if it is not already part of it. If a specified name does not resolve to a measurement, then Nothing is returned; if a specified ID does not resolve to a measurement, then an error is returned.