I am not sure I understand the difficulty. However, I drew a rectangle 2' square. I then invoked the tape measure tool and started a measurement at one corner and began a measurement along one side of the rectangle then typed 12"/enter. SU made a guide point at 12" from the starting point. Then I typed 14"/enter and the tape measurement moved the guide at 12" to 14".
I know that users of cad programs must "tab" to the dialog box which I think is what confuses many people. I noted that once a tool is chosen the type of information to be input appears next to the tool bar input box.(measurement, angle,length etc) after an initial selection (point, line, surface etc) the field in the tool bar input box turns white. A white box indicates SU is ready for input. You do not have to select the box, tab to the box, click on the box etc. Just type!
You may change the input as many times as you wish as long as you do not move the tool (or as long as you move the tool back after moving it at which point the dialog box will read 0)
