Okay, so you've got a Floyd Rose floating bridge.
There are three places a string can typically go out of tune - the bridge, the nut, and the tuning peg.
A Floyd Rose tries to eliminate them all. It eliminates the bridge by making the player cut the ball-end off the string and uses a pressure block to hold the string tight. This is so the end can't spin and change position.
It eliminates the tuning peg by using a locking nut. If the string is never slackened, the winds on the post won't matter. The tension between the nut and the peg never changes once the nut is locked.
It eliminates the nut itself by, again, locking it down, eliminating the friction of string gliding across nut.
So, if you have a string going flat consistently, it's usually one of two things:
1. It's a newer string and it wasn't stretched properly when it was installed
2. The clamp screw on the locking nut isn't tight.