I see a cup of tea as a blend of yin and yang energy. The water is yin and the tea infusion is yang. Understeeped, too much yin. Oversteeped, too much yang. The perfect cup is a proper balance.
I don't like the idea of using mechanical measuring devices to try to achieve the balance. Eg., thermometers, timers and measuring scoops. I do use a timer sometimes but prefer not to.. usually when I have other things I'm doing simultaneously. I think that a proper cup should be made through listening to the water come to (or near) a boil and knowledge of the different sounds of the water and how those sounds affect tea taste. And simply waiting while the tea steeps and finding a natural timing mechanism within one's mind to understand how time affects the taste.
Nothing is more rewarding than brewing a perfectly balanced cup simply by measuring the right amount of tea by sight or feel, pouring the water onto the leaves at the right time and pouring off the brew at the right time, just using knowledge and perception. You will miss the mark more often when you're starting out but after you achieve mastery of the tea experience I think the cups you brew with only the use of your brain will be better than anything a mechanical measuring device would give you.