As I can not justify the joy of the bridge gauge made by Timbuck (AKA Ken)
I thought of the easiest way a poor guy like me could make something to do the same job.
Parallel lines I though.
3mm mdf I had
Fishing line I had
$2 shop (pound store) compass I had.
Mark even spacings along parallel lines at about 8mm with compass - the fact that all the marks are the same distance apart is more important than the actual distance. About 8mm is just a smidge narrower than I would normally expect to do strings even for a kid's uke. 9mm or 10mm spacing would probably have been better for most purposes.
cut big hole in middle - mine is lop sided because the main use is lopsided.
add fishing line - had to wrap string at ends a bit so lines would not pull to side of hole. The lines all go end to end along back.
The picture shows how it works for a nut on ukulele. Basically line up end points with first and fourth string by putting the gauge an angle. The two middle lines then (if you have made it right) divide the nut equally into 3 giving you your 2 middle string positions. Mark the spots and flip the gauge over and check the marks are still aligned with all 4 strings.
If paranoid check again with a ruler. If even more paranoid check again with vernier callipers.
This one has six strings just in case I ever decide to go that way and the five string position is handy for marking centres on fret boards.
Proper guitar makers also like to build in the string width into their calculations, but this jig could be made to approximate that compensation.
P.s. All this jig needs is parallel lines they don't have to be fishing line. The slots in my egg flip are just a little too narrow to work well but check your kitchen drawer you might have one of those egg slicer things or something equally appropriate. I haven't used the one I made to slice eggs but it may work well for that too.