As I suspected, it sprung back a bit.
So I set the board up with a string line
nose to tail over the deck.
The deck was weighed down with the weights
to the correct measurements.
Then the distance between the string line
and a point on the deck was taken.
The string line was reattached to the board.
Measurements taken and adjustments to the rocker made
by propping up the ends and adding a little weight
to the bottom.