Leveling the gravel boards.

It was important that all the gravel boards be level relative to each other. One was chosen as a datum. We checked it was level in the horizontal and checked we had enough space to get the remaining boards in.
We then wedged the board into the post from the back. Several slices of mdf were tapped  in with a hammer and this effectively locked the board.
The ground was firm but with the huge weight of the remaining gravel boards forcing it down over time we had to be prudent. To ensure the board could never sink into the ground a quantity of concrete was inserted under the board along its length. Next we marked a line around the post using a set square and this allowed us to line up the next gravel board. To set the ends a spirit level was used and soon all the boards were on the same level and wedged in place.