Challenge mode ideas for my game

A little while ago in school I made an application that telles you an (x,y) coordinate on a full screen form. you have to click on the form to guess where you think the coordinate point is. After you click it will show the point and tell you how far away you are. however I am trying to expand on this game. Does anyone have any ideas for a challenge mode.
I already have:
the ability to choose whether the coordinates are in inches or centimeters
The ability to choose whether your cursor is invisible
and I am thinking about putting in a rapid fire sort of thing where you have to guess the dimensions within like 7 seconds or they will change

any ideas??
thx