Sorry. Mine was an addition to what neuro said. It just took a lot more time to peck out my words and then post. I had a monitor that would calibrate correctly, then start to drift off after using for awhile. Not talking about the normal warm up time. Some also have a bigger percentage difference around the monitor itself. Most calibration tools work off the center, but often times (on cheaper monitors) you'll have hot spots or color changes. So long as you know where they are at, you can zoom or adjust the view to get it in the calibrated area. It a hassle.