Relative

On the Design tab, in the Snap group, in the Limits drop-down pane: Click the Relative button to limit the snap operation to a position which is relative to another point. You can constrain the snap operation in the X, Y and Z direction, or any combination thereof, by selecting or deselecting the check box options.

Click on the ellipsis to interactively select a point in the Design Window and then click again to select an offset from that point:

You can then use the Point drop-down to modify the offset XYZ coordinates:

Limits