EA's Jeremy Dalberg has posted another one of his "Five on Friday" Q&A features on the official Ultima Online website.
"Why do I seem to miss so often when using Archery?"
I've seen several variations on this question, so Leurocian scoured the accuracy code for me, and we did not find anything that would specifically affect Archery accuracy (with one exception, covered below.) Accuracy in general is a fairly complex topic with many variables, so it's a tricky thing to test at the best of times. Here's an explanation of the different factors - if anyone sees any results that aren't consistent with this, please let us know!
Attacker's stats: Weapon skill and Hit Chance Increase are the stats the formula uses on the attacker's side. HCI is increased by HCI items and decreased by the defender's Hit Lower Attack, if any.
Defender's stats: Weapon skill and Defense Chance Increase are the stats the formula uses on the defender's side. DCI is increased by DCI items and decreased by the attacker's Hit Lower Defense, if any. (Exception below.)
Barehanded defense: If the defender is not using a weapon, "weapon skill" will be EITHER Wrestling skill OR (Anatomy + Evaluating Intelligence + 20) / 2; whichever is greater (which means that if you have none of these skills and are barehanded, you'll have a functional weapon skill of 10.)
Mage Weapons and Use Best Weapon Skill: UBWS uses whichever weapon skill is highest, and Mage Weapons use Magery (with whatever penalties listed on the weapon) assuming it's higher than the appropriate weapon skill for that weapon.
The minimum chance to hit is always at least 2%. If both attacker and defender have the same weapon skill and HCI/DCI, the chance to hit is 50%.
But wait, there's more!
Attacks can be parried or evaded - those are completely different calculations that happen after the hit chance is calculated. If you're trying to track your accuracy, make sure you're taking parried or evaded attacks into account.
Archery has one more caveat - if you move, it resets the swing cycle. There's only one place where this might break the swing - between the "swing" and the "hit" calculations - and we couldn't make it break in a few minutes of testing, but it's possible that a move could break the swing and it would look exactly like a miss, when in fact the attack was simply aborted. Archers, hold still!
The actual formula is conveniently listed in the question below!