Thanks for your responses and explanations. As herclau noticed the issue can be resolved for this case with some algebra.

My intent was to use this package to figure out required or resulting tolerances for dimensions/specifications of components or assemblies. It can be done of course, but it's a rather tedious bookkeeping exercise. Unfortunately it's also a very frequent exercise for a mechanical engineer like me. I'll try using the package keeping in mind its restrictions.

The SEA package would be more useful to bound measurements and calculations with measurements as mentioned.