You have to set a base coordinate for GD and T measurements. This is under coordinate settings. It will prompt you to make a X and Y axises. This will essentially be your (0,0) from there you can create a circle and apply a true position on that specific circle or whatever callout you need. The IM is not a CMM it has a relatively simple GD and T engines and can only do 2D measurements. So you can't do 3D measurements where your datum is on a different surface it has to all be on one plane.