Quoted from phishrace:

A quality digital level is self-calibrating. People sometimes notice mine says the current temperature when it first powers on. 'Is your level a thermometer too?'. Nope, it has an operating temperature range and it won't work if the temp ain't right. I've checked it against two others of the same model and all three have read the same.
Free Pinguy app does need to be calibrated once when you first install it. Easy to do and also very accurate. Free last time I checked, but only available on Apple products unfortunately. I was hesitant to use digital levels for years. Now, I'll never go back. Modern technology making pinball setup easier.
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Quoted from tomtest:

A word to the wise, I have had this Craftsman digital level for 13 years and always put it away with the batteries in it and they leaked and totally Fuc--ed up the electronics so always remove them regardless of when you plan on using it again.