Currently it is possible to display the assigned material and its values for example density, mass inside the model tree but it is only possible to display the values without the unit of measurement. Right now (Creo 7.0.2.0) there is no way to add an extra column with the unit of measurement next to the value but this would of course be a valuable functionality. To display a value is useless without its unit of measurement.
In this example (without units) it is not really clear how the density of the main assembly was calculated. The values of some parts are pretty much too small to have that result for the main assembly.
Easy to understand if the units of measurement are beside the column (but currently not available). After changing the unit inside the parts from mm to cm the whole calculation is more understandable. The display of the values in general makes more sense if the unit of measurement could be available next to the collumn.
