1. A test and measurement instrument comprising: a user interface including a disparity cursor for selecting a region of a three-dimensional image under test; a processor for calculating a set of difference measurements associated with two or more shift values of a plurality of shift values for the selected region; the processor further including a minimizer for determining a minimum of the set of difference measurements; and the user interface further including a user display and having means for reporting a disparity value for the selected region to a user on the display, the disparity value related to the shift value associated with the determined minimum, in which the means for reporting the disparity value further includes means for changing the appearance of the disparity cursor on the display.