Sparging gravity table

A while back I found a website with a table of how much second runnings to add while batch sparging to hit your target pre boil gravity. I know the texts say to use the same amount of sparge water as mash water, but I like to take the gravity and volume of my first running, take the gravity of the second running, then add the right amount to get my pre boil gravity on target, and adjust boil time to get the volume on target as well. Actually, if I nail the post boil gravity, volume is fine as long as it's close or a little over. Has anyone here seen a table like this? Thanks.

Nope...sounds interesting, but too much gymnastics for my simple brewing style.

The sparge amount is exactly what is needed after the first running.

http://wort.org/decoction-mashing/
http://braukaiser.com/wiki/index.php?title=Batch_Sparge_and_Party_Gyle_Simulator

Thanks for the input and links. I really appreciate the help. I'm still kicking myself for not saving the link to the site I found, but I came across the following discussion from BeerSmith that I think will be very helpful in nailing my pre-boil gravity and volume. It might be overkill, but I want to be a stickler for process control, since my professional background is process engineering. Here's the link to the thread (the meat of the post is from Tom Hampton, it's the longest post on the thread):
http://www.beersmith.com/forum/index.php/topic,9508.msg39762.html#msg39762