Intonation & Bridge position

So intonation, a bit of a black art to say the least, how do you get it right? I have some ideas for 6 string guitars pretty much based on the work done by others and some trial & error but for a fanned-fret Mandocello I have no idea how to calculate that.. But luckily there is a low tech way to do this..

I take no credit for this method, I saw Dan Erlewine doing this in a guitar bridge replacement video.. Basically you make a temporary tailpiece to allow you to string up the guitar and just adjust the bridge by trial & error until the instrument play in tune up and down the fretboard.. Not really a fast process but it works.. So that is what I did.

Of course once I am finished French polishing I'll have to do it again to get the final bridge placement before I drill  holes etc but this was good practice any way and now that the bridge position is masked off I can start finishing. First z-poxy pore filling, then some sanding & on to French Polish....