Calculator work -
Say if there is 1ml of drop-out on the 90/10 test, you times by 0.1
If there is 0.5ml you times by 0.05
If there is 5ml you times by 0.5
etc.etc.
if you want to work out 80% you times by 0.8
Its not complex maths. I generally do the numbers in my head, rather than use a calculator, and im not even that great at maths.
If youre using sodium, then the 5g thing is easy - times by 10 (ie add a zero) and then halve it.