What is the correct proceedure for the setting of hand regulaing valves on evaporaors

one of the systems i look after has three evaps and all the hand reg valves are set to 4.5 turns (since commisioning 1987). I have always wondered how they are set up, i presume it must involve taking temps pressures etc and balancing the evaps acordingly.

i'm not having probems with the current settings i would just like to know how its done.

any advice would be greatly appreciated.