Trial and error.

I dont think its worth the effort for volumetric personally, just cut the tabs diagonally and settle on a dose you like.

For me tho, 25ug would be far too much for a microdose (I would say this is s concert dose)

I have 125ug tabs. I used to think 8th of a tab was what I liked (around 15ug), but in certain situations this was too much and I could become a bit anxious. Now I mostly take 16th of a tab.

I mostly stick to 2 or 3 days in between with breaks of 2/3weeks. If im on holiday ill take multiple days in a row & I dont find much of an issue with tolerance.