You can use mathematic formulas similar to Excel in the dimension texts in Revit projects.
Instead of entering a specific number (length, angle) you can use an arithmetic or conversion (e.g. inches-mm) expression in the dimension text (the blue text). Examples:
You can also combine units or use metric units in an imperial project or vice versa - like =5000-7'5'':
Imperial units (feet/inches) can be entered with single or double quotes as 1'-2'', or 1'2", or 1'2, or just 1 2 in imperial projects.
Revit calculates the resulting value (according to the current project settings) and uses it to change the geometry paramatrically.