I thought this might be useful to some so here it is....
If you want to figure out how much weight is actually being applied to your lift when you leg press, then all you have to do is this
1. get the sled angle of the leg press and take the sine of that angle(SIN button on calculator)
2. add up the weight you have piled on
3. multiply your sine of angle & weight
So for example. Say you have a leg press machine with a 45 degree angle with 900lbs piled on. First you would take the sine of 45, which is .707. Then multiply that by 900lbs. You get 636lbs. So when you have 900lbs on the leg press, you only have 636lbs pushing against you.
This is a big reason why people think there is such a big gap between their squat and their leg press, but in all actuality the differerence isn't as great as they thought.
(Keep in mind that the weight of the sled and drag are not taken into account)