I check seat height while stationary (leaning against a tree or something) with one pedal all the way down. Sit squarely on the saddle as you would while riding and place your heel on the pedal, directly beneath your ankle. If your knee has to bend to keep from taking a large portion of your weight off of the saddle, your saddle is too low. If your heel either doesn't tough the pedal or has almost no weight on it when seated normally, your saddle is too high. Once you get the height set in this manner, the slight bend in your knees as they pass through the bottom of the pedal stroke will be perfectly provided by the bending of your ankle that should be happening at the bottom of the stroke.