Programming for multiple devices- PPI

Hello,
How can you write a program for multiple devices? I mean devices with different resolutions. I found out there is a thing called PPI but couln’t really find a way to implement it.
Lets say I have an object in flash with dimensions 1000x1000.
In one of the devices I would like it to appear 500500, in another one 400400.
Any suggestions?
Thank you in advance.
Edit: Just to make it clear, my aim is to use one flash file and get it to work on different devices without recoding.