In my case 'exact' is a relative term! As I mention my process is iterative, I go a ways and then measure. If the hole is too small, I do a little more. If too big, enh, start another one. But in the end, the dimension is important, but not all that critical, it's just nice to know what it is for exposure calculations. A very gentle teasing with a spinning motion of the needle can also help round the hole.
I assume with the laser drilled holes some sort of industrial numerically controlled machinery comes into play.
Exactly. Puncture lightly, sand down, spin the needle and then I place the pinhole on the scanner and take it into photoshop to measure.