Accuracy, affinity, and hit chance are some of the most important, and potentially confusing, elements of high level PvM in Runescape 3. Given recent dialogue in the community about Aurascape, the poll question on the most recent Runescape survey regarding potential changes to accuracy, and the radical departure in Jagex’s approach towards accuracy in high level bossing situations with Solak, now is the time to detail how accuracy works.
In its most basic form, accuracy refers to the ability to successfully strike your target. In RuneScape, missing does not result in a glancing blow, but instead results in a splash. Your ability does zero damage, and in some cases, such as with auto-attacks, does not increase the player’s adrenaline. Many high level PvMers, and even those new to upper end bossing, have voiced frustration at this all or nothing method for determining hit chance. At a place like Vorago, for example, a player maximizing every available in-game boost—T92 weapon, T99 prayers, Overloads, max combat stats, and a Nihil will only have something like 76% chance of hitting. This phenomenon has made combat auras, available in Solomon’s store via loyalty points, a functional requirement for PvM, especially at team bosses such as Vorago, Nex: Angel of Death, and Yakamaru. In fact, for AoD, many teams forbid players from joining if they are not using a “zerk” aura (maniacal, reckless, berserker). Since these auras are time-gated by the number of months a player has had membership, and cannot be earned in game, this can create an unfair barrier of entry to PvM, and arguably is one cause of atomization-players with a limited number of loyalty points who choose to purchase skilling auras rather than PvM auras may find themselves excluded from top teams despite having the necessary skills, gear, and mentality.
Hit chance is calculated by the following formula: H=Affinity × (accuracy/defense). Accuracy modifiers can either be additive, eg. directly affecting hit chance (H) or multiplicative, eg affecting one of the components of H. I will break down each component. Affinity is probably the most difficult concept to grasp, given its interchangeable use with the phrase “base hit chance” by JMods. Affinity measures the weaknesses of a target, much like the old school style of combat. For example, an NPC might be weak to Ranged, and more specifically weak to Arrows. Anyone who has played the game for a long time might remember changing the style of a weapon between “stab,” “slash,” and “crush,” with the differences making a huge impact. The fact that this system remains in place for affinity calculation in the Evolution of Combat is confusing given that those style options can no longer be manually selected. According to the RuneScape Wiki, affinity operates along the following numbers by default:
Using a specific style can impact accuracy significantly for some encounters. For example, K’ril Tsutsaroth is weak to fire spells, meaning using those spells will calculate hit chance with an affinity of 90, allowing a player to achieve 100% accuracy with far lower tier weapons than they would otherwise need. The majority of high level bosses have an affinity of 55 across the board, theoretically making all styles equivalent. Affinity modifiers, therefore, can make a significant impact in overall accuracy. The special abilities of the Statius Warhammer (+5 affinity), Guthix Staff (+2), the Quake ability (+2), and Book of War (+3) are the most commonly used affinity modifiers, together allowing a player to achieve the maximum possible affinity boost of +10 which can mean the difference between splashing almost a quarter of the time and nearly perfect accuracy.
Base accuracy is calculated by the main hand weapon, off-hand weapons, while having an accuracy “stat” are not part of the calculation whatsoever, which is why (usually) main-hand weapons retain a far higher value. This base accuracy is determined by a formula that includes adding the formula used for how skill level affects accuracy: F(a)=0.0008a^3+4a+40 plus a calculation for the tier of weapon, which looks like this: Accuracy=F(a)+2.5×F(weapon). In the case of a 99 skill level player F(99) comes to 1,212 (after rounding). Using a tier 90 weapon, (2458 base accuracy), we can see that their accuracy comes out to 3,670. Multiplicative modifiers such as overloads, extreme potions, or accuracy boosting prayers that change the player’s level can make a huge difference. This is the reason “zerk” auras such as maniacal are so impactful. A player with 99 magic using a Supreme Overload and Maniacal will have a base magic level of 128. Using a tier 90 weapon again as an example, their base accuracy would then be 4,687. After this formula is calculated, additive bonuses come into play—Nightmare Gauntlets, Reaper Necklace, Nihils or creature specific boosts such as the Balmung vs Dagganoths. Skill level plays a huge part in determining our accuracy rating. Given that Saradomin brews lower our base level and most other types of foods cost adrenaline, the most effective way to increase kill speeds is by learning to consume as little food as possible (or swapping everything for Jellyfish) through using optimal rotations, prayer flicking, and defensive abilities.
The final piece of the puzzle is defense, which is mostly static. An NPC’s defense is determined by their armor rating and the armor rating bonus from their defense level. These ratings are easy to access on the Runescape Wiki. Let’s take Telos as an example, whose armor is 1,924, affinity is 55, and defense level is 80, which gives a base defense of 2,694. Using the above numbers, a player with a tier 90 weapon, overloads, and maniacal would have a hit chance of 55 x (4687/2694), which equals 95.6 percent accuracy. Without the use of overloads and maniacal, however, we can see that accuracy drops to 74.9 percent. The ability to modify affinity can lead to even better results. If we add a +2 affinity for the Guthix Staff special attack, our accuracy comes to 99.1 percent. For group bosses such as Nex: Angel of Death or Vorago, where base defense is far higher (3636 and 3161 respectively) these changes to affinity and the use of zerk auras can have a tremendous impact, which is why at least one team member typically uses the Statius Warhammer special attack for the +5 affinity. The combination of increased affinity, overloads, t99 prayers, and maniacal can result in 100% accuracy.
Understanding the different components that factor into determining hit chance is vital for advancing as a PvMer in Runescape. Knowing when to prioritize affinity modification, what aura to choose, and even which weapon to bring can make vast differences in kill times at a boss. As anecdotal evidence, my Telos kill times with affinity changing weapons and maniacal are around 4:30-5:30 on average. Using the same methods, gear, consumables and rotation without an accuracy boosting aura slows my kills down to around 8-9 minutes, which drastically changes the GP/hr at the boss. In my opinion, the current method for calculating accuracy is good—there are many factors and lots of room for growth and complexity e.g. more creature specific weapons such as the Darklight or the Hexhunter Bow. The problem, however, is that splashing is too penalizing. Even taking into account every single possible boost, drinking a few Saradomin Brew sips to lower your levels and therefore drastically impact accuracy can mean a much slower, or even a failed kill because splashing is the same as a zero. Making every boss like Solak, where defense is far lower therefore eliminating splashing, is one potential solution, but could great damage the balance of encounters such as Vorago or Telos. Instead, I would argue for a system that penalized “splashing” with a lower ranges for damage. This would eliminate the frustrations of splashing multiple hits in a row at crucial moments simply due to poor RNG. While the scope of such a project would require a tremendous change to the combat system, I think it’s vital for the health of combat going forward. To put it simply: splashing isn’t fun.
 Runescape Wiki. “Hit Chance.” http://runescape.wikia.com/wiki/Hit_chance