Originally Posted by ls01

mark the seat post with some tape. put it right on top of the seat post collar.
loosen the seat post clamp. extend the seat post an appropriate amount.
clamp seat post in stand and repair bike.
remove bike from stand. loosen seat post collar clamp.
reset seat post to marked position. tighten seat post collar clamp.
If bike is carbon do not exceed the torque specification for your bikes seat post clamp.
ride the shiz out of it.