correct chain length

I need help/advice:

I have been working on my cannondale jekyll 1000 w/rear susp frame and I am trying to set the chinlength, but I am confused.

According the shimano rear drivesystem, it says that for the correct chain length, set the chain on the largest chainring and largest rear cog and add two links.


But according the bike's manufacture, it says that the gearing combinaitons of the smallest front chainring/smallest rear cog, and the largest chainring/ larest rear cog should never be used. These gear combination (called "cross chaining") place undue stress on the chain, chainrings, deraillerus, and rear cogs. And that similar ratios can be achieved in other combinaitons using the middle chainring.

How do I go about this, do I use use the largest chainring and largest rear cog with shock in most forwarded position (steepest); or do I use the middle chainring with largest rear cog; Where should the shock be position when setting chain length?
How do I set the correct chain length?

Please help> thanks