Photoshop Elements :: How To Move Cursor Digitally Not By Hand Motion

For cropping  part of an image, the cursor virtually snaps to positions according to what the programmer sees in the image.  Maybe not always, but that is the way it seems to me in many cases. Even when it does not do so, I find it impossible to move the cursor in very tiny increments by using my mouse. If I were to greatly enlarge the image on the screen to get finer control, then only part of the image would fit on the screen. I want a technique for controlling the selection with as much fine precision as is available when resizing, for example. We can specify hundredths of a millimeter when resizing; very finely precise indeed.
 
Is there a technique that I can use to have very fine and precise control of a crop, preferably by specifying a movement left-right-up-down using decimal fractions of a unit of distance?  The same question applies to using the selection tool.