Heroes and equipment all have elemental resistances, but a hero's intrinsic resistances and those of all the equipment they are wearing need to be combined into a single value per element. This menu lets you select from one of three different formulae to use for this.

The currently selected formula is highlighted, while the others are darkened. Move to a formula with Up/Down and hit Enter to make it the selected one.

* Old awful formula
 This is the default for old games for compatibility reasons, but you should never use it if you have a choice, because it causes down-right stupid results in a number of ways!

* Combine by multiplication
 This multiplies together all input values, ignoring negatives. Then, if any of the input values were negative, the result is negated. This means that if anything was set to 0% damage, the result is always 0%, and otherwise, if anything was negative damage, then hero always absorbs damage from that element. Note that weaknesses (values greater than 100%) can stack to huge values!

* Combine by addition
 This adds together the differences from 100% of all the values. Equipment elemental damage is displayed differently when this is selected: 100% becomes +0%, 150% becomes +50%, etc., so that you can simply add together all the displayed values.