Magical weapons what is that percentage all about?
That is percent of the weapons power. For example, if a weapon says it has 80% power, it is doing 80% of the damage it can do. A weapon can be used to its full potential only when your character has a high magical aptitude. How high your magical aptitude has to be before it is 100% depends on the weapon. If your character is very technologically inclined, it will be 0% and I don't think you would be able to use it at all
It's the same way with technological weapons too. Magic-inlined characters suck with them.
It is the nature of magic and technology in Arcanum.
