Aaand docs again.

osu.Game.Rulesets.Osu/OsuDifficulty/Skills/Aim.cs

@@ -6,6 +6,9 @@
 
 namespace osu.Game.Rulesets.Osu.OsuDifficulty.Skills
 {
+    /// <summary>
+    /// Represents the skill required to correctly aim at every object in the map with a uniform CircleSize and normalized distances.
+    /// </summary>
     public class Aim : Skill
     {
         protected override double SkillMultiplier => 26.25;

osu.Game.Rulesets.Osu/OsuDifficulty/Skills/Speed.cs

@@ -3,6 +3,9 @@
 
 using osu.Game.Rulesets.Osu.OsuDifficulty.Preprocessing;
 
+/// <summary>
+/// Represents the skill required to press keys with regards to keeping up with the speed at which objects need to be hit.
+/// </summary>
 namespace osu.Game.Rulesets.Osu.OsuDifficulty.Skills
 {
     public class Speed : Skill

osu.Game.Rulesets.Osu/OsuDifficulty/Utils/History.cs

@@ -40,7 +40,7 @@ public T this[int i]
         {
             get
             {
-                if (i > Count - 1)
+                if (i < 0 || i > Count - 1)
                     throw new IndexOutOfRangeException();
 
                 i += marker;