Guitar Maintenance Set-up & Intonation
In the tuning section I briefly discussed the physics of string length, tension and the resulting frequency or pitch. The theoretical position of the saddle on the bridge is exactly double the distance of the nut to the twelfth fret. For an accurate measurement measure from the forward edge of the nut (the edge closest to the frets) to the center of the fretwire. Do this in a straight line, the same line of the string. Any increase in tension on the string will raise it's pitch. When you press the string down against the fret you are increasing the tension and bending the tone sharp. The idea here is to compensate for this increased tension by lenghthening the string. This is done by moving the saddle farther away from the nut. This is called String Length Compensation or setting the intonation.
Before you begin the first thing to remember is that Everything Effects Everything. What this really means is any adjustments made to the guitar will change the intonation so adjusting the saddle position should be the last thing you do. For now let's assume everything else has been done. The truss rod adjustment, the slots in the nut are spaced right and filed to the correct width, angle and height. We want to work with a new set of strings of your brand and gauge. Electric guitars usually have adjustable saddles at the bridge. We'll talk about these first.