> "it seems very reasonable to design a shower valve that is biased for human temperature preference" It's not that simple. Hot water temperature varies greatl

> "it seems very reasonable to design a shower valve that is biased for human temperature preference" It's not that simple. Hot water temperature varies greatly from one home to another. Cold water temperature varies tremendously from summer to winter. Take a picture of your shower control for the same water temperature in winter or in summer. You will see it's not turned at the same angle, because in winter you need a lot more hot water to balance the ice cold water from outside (especially if you live in the country, it will be ice cold, trust me). As a consequence, the part of your shower control that you call "confort zone" can be almost 100% too hot or 100% too cold in another home or in another season.