I never measure my Shocks. How I do my shocks is I set my droop... then I set my ride height via the shocks. For 4mm I set the shock threaded screws to make sure that I am getting 4mm. I get both sides to be 4mm and then I measure the distance from the top level part of the Shocks to the top level part of the threaded collar. I make sure that both sides are even. If they are not really really close then my chassis is tweaked and then I fix that. Measuring your shocks do nothing unless you are trying to acheive a ride hieght.
Mike Webb