Having always considered I have good intonation skills my Giannini Craviola has baffled me until yesterday...I discovered that the nut end(0)is not square...now should I angle the nut back on the bass side or deal w/it at the saddle? I inserted a shim in front of the nut(bass side) to push nut back.So far this works and cleans up the tuning ok. What would you do? I had been looking at this for over a year w/o measuring(state of denial).
The worst I've seen was on a 1960s Gibson acoustic - the end of the fingerboard was cut at a crazy angle, so I had to bring it forward about 1/16" on one side to set it parallel to the first fret.
Lots of builders now reduce the nut-to-first fret distance by as much as about .030" to reduce sharping in the first few fret positions.