Throwing Power - The throwing power of a thrown weapon is the weapon's power bonus or the character's size - whichever is greater - plus the number of hit points used to increase the damage.
Maximum Range - The maximum distance you can throw a weapon is the throwing power of the attack multiplied by your natural reach plus any reach added by a sling or spear thrower used to throw the weapon. The thrown weapon's reach bonus is not included.
Optional Ability-Based Extra Distance Rule - Add 10% to the character's reach for throwing purposes for each level of throwing ability (plus the bonus of one skill if any applies.) A half level adds 5%. This reflects special types of strength, flexibility and coordination which contribute specifically to throwing ability.
Slings and Spear Throwers - Slings and spear throwers add to your reach to determine maximum range. They usually also change the heft and damage bonus of the thrown weapon.