This adjustment requires a helper, too. Place your bike on a level surface next to a wall or post so you can hold yourself upright (or put it on a trainer, but be sure to level the bike). Put on your biking shorts and shoes, get on and pedal backwards until you're sitting in the "sweet spot" on the seat. Move your feet into the position shown in the photo. The forward crankarm and pedal must be level with the ground. The fore/aft seat adjustment is correct when a plumb line (any piece of string with a weight on the end) hanging from the bony protrusion just below your kneecap, bisects the pedal axle.