QuadLevel is the ONLY level on the app store that simultaneously gives you four displays - horizontal, vertical, diagonal and 2-D. Unlike other levels, it responds quickly without the bubbles jumping around randomly.
QuadLevel is also unique in that its horizontal, vertical and 2-D modes tell you in centimeters per meter OR inches per 10 feet how far off you are from level or plumb. This allows you to figure out where a long board or countertop will end up - without having to do trigonometry!
Since QuadLevel is accurate to 1 inch per 10 feet (less than half a degree), it's also the most accurate level available on the app store!
Calibration takes only seconds, and is simple and user-friendly, complete with an amusing sound to let you know when it's done. There are many levels out there, but this is the only one that has everything.