question about armor imposed mana points penalty

[tg122]

hello,

I'm new to Angband, and have been unable to find any information regarding a certain question. Can somebody tell me how the armor penalty that reduces your mana points works? Are there any factors that affect it? Does the amount of armor you can wear without having a MP penalty increase with your character level? I'd appreciate the help, I looked in the help files and searched the forum but haven't found anything yet.