I was a user of the trial version with no problems (apart from the limitations of the trial version). Since I upgraded to the paid version, the Calipers no longer appear when started. I get a button in the task bar showing the calipers are "open" and the icon in the system tray is present, but the calipers themselves are nowhere to be found, therefore they are unusable. This is not what I was expecting when I made the purchase!

Can someone please help me get my calipers back? I miss them!

If you click the Calipers icon in the system tray choose 'Center in Window'

I tried that and I still can't get them to appear.

I'd try a reinstal

I tried that also. I even tried downgrading to 3.2 and no dice. Back to 4 now, but they just won't appear!

Do you have a dual monitor by any chance?

Yes I do. Does that prevent the calipers from working? (It worked when I was using the trial versions, though).

No it won't prevent it, but if you add in monitors with the Calipers running then they may drop off the screen. I'd restart your computer, then that should fix it. If that doesn't work do a full reinstall, delete everything in your Program Files/Screen Calipers folder first,