We use 3rd edition for book rules, (4th ed was too thorough with its different types of books). All studying is done via full-level advancement of Arts and Knowledges. If the art-book you're studying is three times your current score, you gain 3 levels. If twice, 2 levels and if it's just over your score, you gain one level. Books of knowledges work in the same way, only that you gain experience points and not levels.

4th Edition (We don't use Grog Status Virtues or Flaws)
Character creation is done according to 4th edition, but we have some of the virtues are modified and some are from 3rd edition. Our version is a mix between the 3rd and 4th edition.

New magus characters receive a few improvements. See the rules for new magi for more information.

We use our own set of rules, composed of 3rd and 4th editions, with emphasis on 3rd. You can view or download the combat rules here.
[ View | Download (PDF) | Rules with covers (PDF)]

3rd Edition
Confidence points can be used to reroll an unsuccesful roll. If the reroll succeeds ("success" determined by SG), the point is regained for the start of next session. If reroll fails, point is lost permanently. Confidence can never decrease below 1, except in extremely demoralizing conditions (slavery, losing your soul etc.). Confidence points can be gained (awarded by SG) by exceptional demonstrations of bravery, succeeding in a very difficult task etc.

4th Edition
When creating an invested device, open it for enchantment normally. You can fit [(material × size) × vis] × 10 levels of spell effects in it. (wooden (2) staff (large, x4) can contain 80 levels of spell effects) Spell effects are not rounded up to nearest 10 levels, device can contain effects up to its maximum level. (25+12+13 = 50)

New magus characters receive a few improvements. See the rules for new magi for more information.

Shorthands need to be translated (Intelligence + Scribe Latin + stress roll against 6+ to know Tech & Form and level. If a magus has deliberately scrambled his own shorthand, the roll is against an ease factor of 9+. If you have once cracked the code of the certain magus, you get +3 to this roll. In the case of botches, there are no additional dice from the Aura.

When magus cannot use voice (gagged, Twist of the Tongue, Captive Voice) or gestures (bound, hanging on a ledge, spells like Veil of Invisibility and such) he suffers the same penalties as if he had cast the spell silent and/or without gestures. Virtues like Silent and Subtle Magic work normally.

4th Edition (Veil of Invisibility -> PeIm15, due to complexicity).
Use of Passivity of the Spell Casting Wizard (WGre) is denied (see Spellcasting, above).
Call to Slumber and Scent of Peaceful Slumber work instantaneously like they should, not after 5 minutes or after the fog has risen to target's nose level. This is due to guidelines, which say that ReMe10 spell controls target's mental state. This happens immediately, not after a certain time.

4th Edition (+3rd Edition, if it's not in 4th)
We also have a few house virtues, detailed below. And of course the famous Real Life Virtues.

We have (actually Lauri, our SG, has) divided the weapons to new groups and skills. Some examples include Bladed weapons, Crushing and cleaving weapons, Flexible weapons and so on. These are explained in the combat rules and its html-counterpart. We use dodge and brawling to avoid getting hit (when fighting unarmed). With equipped weapons we use weaponskills to defend.