The level I linked above is self-calibrating. When you power it up, the first thing you see is a temperature reading. This is done to insure the level is being used within it's proper temperature range. If it finds the correct value, the temperature is no longer shown and the current pitch or level is shown. Not sure what the temperature range is, but I've never had mine not power up properly.
When leveling, the level display shows arrows to tell you which side is high or low. Makes it simple to know which levelers need to be adjusted. The accuracy, 1/10th of a degree, is perfect for pinball. Any finer and it would be too fine. Hundredths of a degree is too fine. Any less and you couldn't set pitch to 6.5 degrees, which most modern games should be set to.
Checking level with a bubble level you can get it close. Checking pitch with an analog angle finder is not accurate at all. I wasn't a big fan of the digital levels either when they first came out. Now I won't do it any other way.