If you are belaying off of the anchor then the tension in the rope and the force on the anchor is equal to the force exerted by the person at the end.
[edited to change:] With a redirect belay (and no friction) the tension is equal to the force exerted by the belayer plus that of the climber which is approximately equal to the force on the anchor.
With a redirect belay the tension on the rope is still the same since the climber is not accelerated but the belayer end of the rope has the same tension as well. This puts twice the force on the anchor. [/edit]
Geometry and friction modify this force. I think biners are like 60% efficient as pulleys so it only requires about 60% of the force of the climber to hold her.
I hope that's what you were asking. Majid brings this up all the time so I'm sure he's proud of you for asking.
(This post was edited by hafilax on Oct 7, 2008, 5:16 PM)
Post edited by hafilax
() on Oct 7, 2008, 5:16 PM: My original idea of tension was wrong.