LOL! yes sunstone is in my arsenal, uhm, actually two, one is only 12x18x4mm and bit small to work
I have made, bought or at least handled just about every instrument i have found documented enough to replicate, shadow-boards, sun-compass...
I have a father in law that is a cabinetmaker and I am myself traied as instrumentmaker (scientific instruments, theodolite, barometers...) so together we have been able to replicate such things as wooden octants, backstaffs, crossstaff, khamal, shadowboard, something like five or six suncompasses, quadrant, mariners astrolabe, nocturnal and several more with decent success.
oddly enough the khamal is usually within 11', pretty impressive for a home made instrument consisting of piece of wood and a string.
sad part with the high precission khamal was that I had to cheat and use synthetic string (40kg spiderwire fishingline in this case as it was on hand), the natural fibre I originally used reacted too much to humidity and kept changing length on me throwing the original calibration out by almost 30'.
Oh, check this out if you like astronavigation, it is a shortstory (which is a decent tutorial in terrestrial astronavigation by the way) and a copy of the Bowditch long term almanac as PDF, great to print a few and have around
AmeriSurv.com - Long Term Almanac, or, what to do when you can't use your total station and GPS