Whatever your theory/"ingame script description" is, in practice it is as follows:
120 - is base crit rate for bow/dagger. 40 is for blunt/fist, 80 for swords/polearms.
Then you need to adjust it with DEX modifier. DEX — База знаний Lineage 2
So, having 30 DEX you'll have 1.1 multiplier.
Resulting formula is
crit_rate=base_weapon_crit_rate * dex_mod * (1 + 0.3(focus) + 0.3(crit chance) + ...) + static modifiers(master critical, augmentation static bonus, SA ability bonus, etc).
This game has so much description bugs and uncertainties, that you must check everything by hand. For example, counterattack of GH says it "reflects melee skill damage", while in reality what it does is: upon melee skill usage on you, with 90% probability, it performs a COUNTERATTACK on the enemy, where damage dealt = 1189 * user p atk / attacker pdef. And not only that, description doesn't tell you it does this thing only if skill being used doesn't contain a debuff. So hammer crush or sting won't get counterattacked. Also it doesn't say about counterattacking dagger abilities twice, and even triple for backstab/blinding blow. Also description doesn't say skill won't trigger any counterattack, if it has +DUEL(pvp damage) enchantment route. And last thing - counterattack gets triggered even if ability missed(due to ultimate evasion or simply dagger random). Also note that if you don't have much p atk(disarmed) - counterattack will deal almost no dmg, while being equipped with a bow(highest p atk) makes you counterattack like a monster.