The best way to get accurate readings when setting intonation is to use a good-quality strobe tuner. This is because strobe tuners act as a magnifying glass when tuning a guitar. If you break down the interval in between two notes into 100 separate intervals, called cents, you will be tuning with very fine precision. A strobe tuner makes this possible. If you can adjust the 12th-fret strike tones within 5 cents of the open strings, then you will end up with a guitar that will play in tune. And it will stay in tune all the way up and down the neck (that is, with a fretboard that is properly slotted and frets that are properly crowned). If you have a guitar that has separate string saddles like a Strat or a Tune-O-Matic bridge, then this is a very easy process.