I'm new to Tinkercad, but so far I haven't found an easy way to select an object that's obscured by other objects. For example, an object that's inside another object. It would be great if pressing <TAB> cycled the selection through all objects one at a time. Or a dropdown list of objects that I could name and select from. It could even be a nested list, based on groups of objects.
The only way I've found to edit internal objects is to move stuff out of the way, measure/edit/duplicate the object of interest, then move everything back together.