And if you need that value within your model, you could store that it in a tagged value associated with the element or association it has some context to...
I often use tagged value as containers for metadata that is derived via scripts an example might be the "completeness of the specification" of one of my elements... (say from a scale of -1 to 4 or an enumeration of n/a, not started, incomplete, acceptable, completed; then using a shape-script altering the elements color or other adornment visually to indicate the status...)