In game design, it has to be stated whether it’s multiplicative or additive. Sometimes a logarithmic function is used as well, with increases in efficiency as 1 / ( 1 + bonus ). This allows you to always add more bonus, but there’s diminishing returns.
This upgrade adds +100% critical chance.
The weapon has a base critical chance of 10%, so the new critical chance is 20%, not 110%
i wish it was more common to also indicate the precedence of a percentage increase, so that it’s easier to know if i’m dealing with (x + y ) * z or x + (y * z). although that’s admittedly a lot harder to communicate.
Just include a glossary of formulas for figuring out stats/chances/whatever in your game. With clearly labeled variables. Then throw a reference to that glossary in your tooltips/helpful popups.
