For un-cased beef snack sticks and ground or whole muscle beef jerky in my smoker, I go by color change to the deep mohogany from smoke, which also indicates that it is in fact drying, to texture checks. If you pinch a piece and it is firm, it's close to dry. If it feels soft, it needs more time. When you do a bend test, it should bend in half and crack when folded at the bend. If it snaps/breaks before it's folded in half, it's drier than it needs to be, but no harm is done. Drier meat is preserved for longer periods of storage, if desired.
My final poduct check is weighing the poduct before and after drying. If the combined weight of the dried product is 50% (+/- 2%) of the starting weight for 85/15 ground meats, then I'm within my own preferred tolerances. 48% is fairly dry, while 52% is just a tad moister than I like, but still OK.
If you're weighing your meat after it's mixed/cured, but immediately prior to starting your smoke or drying is the key. Then immediately after you pull it from drying.
Heres a link to the most recent whole muscle jerky I've done...it covers quite a bit of the actual drying, pics of what things were looking like, texture checks, and the final product dried weight ratio:
Hope this gives you some extra insight for your next run of dried meat...