Due to my past work of research engineer in physics and chemistry, I like to experiment with tea with precise tools. So digital scale, timer and digital thermomether.
When I have a new tea , I always test it with scale, thermometer and timer. Usually I brew the tea two different ways simultaneously and compare.
After having determined the best brewing method (according to my taste), I continue to use the scale (handier than remembering how many teaspoons I have to use with each tea) and the timer (I don't wear any watch) but I use the thermometer constantly only for gyokuro.
For puer, I have a more empiric approach: no scale (when you break a puer cake, you can't adjust the size of the pieces you get) I try to determine from the look and taste of the infusion what time is needed to the following one (which I am not always very good at...)
This morning Keemun for breakfast and Jasmine pearls right now. (No scale needed for both teas as I drink them regularly)