Adjusting the length of the B-string for proper intonation. The note at the 12th fret was sharp so I needed to shorten the length of the B string. This is an adjustment of small increments - even half a turn of the screwdriver could make the intonation flat. Additionally, while it retains the "Vintage Vibe" the 3-saddle bridge does have some limitations - such as lengthening the string to intonate the B string also affects the high E string. Sometimes a "flat - sharp" compromise is needed. More information on intonating a guitar can be found at Fender’s Website - Intonation and at Fret Not Guitar Repair – Intonation.