Detents are a mixed blessing. If they are correct it can save you a little time. If they are off then
they'll obviously be deceptive. And if you need just a tiny bit of correction one way or the other from
"zero", there will be a temptation for the detent to kick in anyway, and it will be hard to hold the
adjustment. Detents also have a tendency to wear over time. So I never wholly trust them, even with the best of cameras. As already mentioned, it is far more important to check focus visually across the groundglass plane itself with a good loupe. And if you need to be fussy with verticals,
use a groundglass with lines on it.