In your opinion, why are a person's hands a useful tool when estimating a serving size?

Our hands are very useful when it comes to measurement of sizes, though it's not that accurate, still it can give us a very close measurements especially in a serving sizes.
Example of serving sizes:|
-our palm is the measurement of protein portions.
-Our fist is for the veggie portions.
-Our cupped hand is for the  carb portions.
-Our thumb is for the fat portions.

Ais the answer hope this

Answer its calculated by subtracting your age from 220;