I agree with Wick, I have and use both. I carry a time piece when acting as a sergeant, but when I am acting as a rifleman or in a relaxed setting, the sundials work easily for half hour increments, and you can learn to do fifteen minute increments.
You have to know the declination (the error between true and magnetic north) of your location OR you need to compare the sundial to an accurate time piece, once.
You line up the compass with magnetic north, and if you were actually going to navigate with it you'd need to know the declination anyway...,
..., so you line up the compass with magnetic north. Then compare the sundial mark and the time it indicates, to the actual time. Next, rotate the sundial until it shows the proper time (hint this is best done on the hour), and you will know the "error" of your compas at magnetic north, and if you note how far right or left of magnetic north that you have to hold the compass, you will then be able to do so later in the day when using the sundial without cross checking on a time piece. Once you have that for the area where you normally do your historic stuff, you don't need to do it again, especially if you mark the compass, unless you change your geography by a good amount East or West.
OH don't forget to apply daylight savings time when that's in effect. :shocked2:
LD