What are you trying to do, see if the neck is bowed? You don't need to press down the strings for that. Hold the guitar up and look at the neck, from the back of the body, looking forwards to the headstock. Check each side. The strings are in a straight line; you'll see if the neck itself is straight, inbowed, or back-bowed.
Pop a capo on the first fret, then depress the string at the body fret (the strings should be at your normal tuning). With a set of feelers guages you should get a relief of between .008-.012" at the 7th fret. If you adjust the truss rod, never more than 1/4 of a turn and give it 24 hours to settle, before checking it again to confirm measurements as above. Any other adjustment (bridge height, nut slot depth) should be done after the neck relief is set.
The numbers are a good "starting point", but as Blueman said, play it and see how it feels to you...that is the ultimate setting of the truss rod. But as Chris of Arabia said, you also need to consider the nut and bridge settings after you adjust the rod...especially if you are making your adjustments as Blueman said (and as I do)...by the way it plays and feels to you.
I never measure it, I go by feel. I play the guitar a little, put it thru it's paces, and see if I need to adjust the truss rod or action.
That's the way I do it it as well. Some guitars play better with more or less relief, some play better with lower or higher action. You have to take the time to find where the guitar "wants" to be played!