Calculate average percentag with angle difference.

Hello everyone, i am having a problem figuring out some math.

I am trying to set up a calculation, that outputs the total accuracy from a range of values given.

Lets say the values are: 20, 5, 32, 60, 100

If a value is 0, it is 100% accurate

If a value is 180, it is 0% accurate.

How would i go about doing this?

Thanks!

Maybe this?

(1-value/180)*100