I donno about "measuring" ...
But I would check the "C" channel/track for a pinch near the bottom. See if it's collapsed in any way and run a spare roller up and down both channels with the door in the UP position.
Next, I would check to see if the "C" channel is just a touch off vertical close to the bottom/floor end. This allows for a better seal condition at the base. I think that's the way mine are anyway. There's a little play at the TOP, but not the bottom. The rollers have enough play end to end to compensate for any misalignment in the other vertical axis. So, bring a 6 ft long level and a measuring tape or story stick if you have one that long.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
Last edited by woodnthings; 08-01-2016 at 11:33 AM.