Resistance is a measure of a characters protection from an attack of a given attack type. Resistance can be provided by race, equipment, magic or potions. Resistances derived from potions override any existing resistance.

Protection is a positive increase in resistance and is calculated using the following:

total protection[attack_types] += ((100-current protection) x additional resistance) / 100

so if a player has 30 fire resistance and casts the spell Protection from Fire and gains 60 more fire resistance, their total protection would be:

total protection[fire] = 30 + ((100-30) x 60)/100
total protection[fire] = 30 + 42 = 72

As can be seen, the more sources of protection a character has, the less partial resistance each item affords. It is therefore impossible to reach 100 protection without an item that grants 100 protection. Protection cannot exceed 100.

the same formula applies (in reverse) for vulnerability:

total vulnerability[attack_types] -= ((100-current vulnerability) x additional vulnerability) / 100

so if a player has -5 resistance from their god and -15 resistance from their weapon:

total vulnerability[fire] = -5 - ((100-5) x 15)/100
total vulnerability[fire] = -5 - 14.25 = -19

As can be seen, the more sources of vulnerability a character has, the less partial resistance each item affords. It is therefore impossible to reach 100 vulnerability without an item that grants 100 vulnerability. Vulnerability cannot exceed 100.

Resistance is the total protection minus the total vulnerability:

total resistance[fire] = total protection[fire] - total vulnerability[fire]

Combining the above scenario, the player would jave:

total resistance[fire] = 72 - 19
total resistance[fire] = 53

It should be noted that vulnerability cannot be easily overcome by additional resistance and can have a significant impact even from small total vulnerabilities.

There is a resistance category for each attack_types. The only exception is Armour which works exactly the same way but resists physical damage.