Quote Originally Posted by pdeeh View Post
I can accurately weigh chemicals
You can weigh chemicals accurately but you may or may not know the exact composition of them. Most chems are only of technical purity, and whatever else comes with them can change the final result.

Quote Originally Posted by pdeeh View Post
Perhaps for more commonly used developer formulae which were intended to be made up by hamateurs, there is a bit more leeway in the pH range they will tolerate?
Wasn't it quite common to have a stock solution of 1% KBr or whatever back then (I wouldn't know but the Darkroom Cookbook suggests so)? And weren't published dev times generally considered starting points from which people had to fine tune to their needs individually?

What has changed is that we have dozens of films and hundreds of developer recipes readily available, yet expect usable results from random combos at the first attempt.