Looking at a leg press weight of, for example, 700 pounds let's calculate the true resistance: Without explaining too much about the equations for the calculation we find that:
F = W sin 45
where F = actual force generated, and W = weight (700 lbs), and "sin 45" accounts for the angle of force generated compared to gravity.
Therefore:
F = 700 (sin 45)
F = 700 (0.707)
F = 495 pounds of resistance.