Just spotted this G-C...is it totally resolved? (pun?)
The Ctl zoom system is very handy, I use it all the time for proof-reading :-)
However, it can lead one astray as it is program-specific. ie. you can come out of Pprune and go to a standard res screen in another program, but when you go back 'home' to Pprune, you will find it's small again. Ctl 0 (zero) is the datum reset.
This should only leave the task of finding the Native resolution, which I'm sure you ascertained on day one.
LR