Calculated values are updated when new characters are entered.

You can choose between:

•  a=1, b=2 ... z=26

• a=26, b=25 ... z=1

• abc=2, def=3, etc. (phonepad)

Sum of char values is the sum of all character values without further processing.

Sum of digits of sum is the sum of all digits of the first calculated values.
So if the sum of char values is 82 then this value will be  8 + 2 = 10.

Reduced to one digit is the value you finally get when repeating the process of adding all digits. So in the example case listed here this value will be 1 + 0 = 1.