This does not work well as you want 50% on the slider to somewhat be perceived as half as loud, this is why the exponential formula that has been posted multiple times works better.
Even if the user is given the approximation formulas like volume^4 or 33*log10(volume/100) where volume is a value between 0-1, I still get the feeling most probably still wouldn't be able to apply that knowledge to their own projects themselves...
This is why I think Construct should provide an alternative (non exclusive) option to perform this task automatically, (please, let me repeat the keyword: automatically), without the users having to manually type complex mathematical formulas and try to understand and apply them correctly for something as common and necessary as controlling the sound volume in any game.