I'm trying to add a sensor in a part file so that a dimension doesn't go below a certain value.  When I select Sensors/Add Sensor and then select Dimension as the Sensor Type, I can't figure out how to get the Properties box to populate.  There are no dimensions in the graphics area to select.  It seems this should be a simple thing to do but for some reason it doesn't seem to be working correctly.  I'm using SW 2010, SP 4.  Thanks in advance for the help.