Hey I'm just wondering if there is a rule for how high to position your saddle.

I was under the impression originally that it was a matter of:
1. Comfort
2. Having your knees just short of straight when in the down
position.

Then I was reading a formula in a book which told me to measure my inseam in cm and multiply it by .0883 and then take the answer from that and measure in cm from the center of the BB to the top of the saddle and position it there.

Upon doing this I had to lower the seat from where I positioned it originally (thinking comfort, etc) by at least 4 inches. (yes, inches, I had to convert to/from metrics due to not having a metric ruler and the formula was metric)

What is right? I immediately repositioned my saddle due to the awkward position it put me in and all of the pics I've seen and other riders I've seen show people in the knee near straight position. Is it different for street and trail riding?

Help. Thanks.