Throwing Power - Throwing power is the hit points you use to cause extra damage, plus your size, minus weapon heft, or your maximum throwing power (the hit points you use to cause extra damage plus 5) - whichever is lower. If throwing power is zero or negative then you can't throw the weapon.
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.