We display fullscreen data in a projector whose source is the secondary monitor. Sometimes the picture of the projector cannot be viewed by the operator of the computer so we need a control window on the main monitor where we can see what the projector display.
Is there such a program? Something like the little live preview in the Windows taskbar, when you hover over a program, or the magnifier app that you can dock and place the cursor in the second screen.
Only requirement is that is should be free.