From Ars Magica
Novice armor is the most basic of the Ars Magica armors. It offers protection equivalent to Leather Armor.
Apprentice armor is designed to be mana stable around magic level 6 with a full set.
If damaged, it will drain mana from the wearer at a rate of 0.02839975 per tick per piece worn in order to repair itself.
With a full suit with damage, your mana will be draining at a rate of 2.27198 mana per second.