The core comes out of the ground, YOU mark the top of it as the depth of the bottom of the previous trip and the bottom of it as the depth reported before the driller came off bottom. You make the same markings on small wooden blocks that you will insert at the top and at the bottom of the core when you place it in the core box/boxes. You take a black and a red permanent felt marking pen and you run a red line and a black line from the top to the bottom of the core with the black always on the right and red on the left. In your notes you note the amount of core recovery for that trip as a percent. Drill 10 feet got 8 feet, had an 80% recovery. Now if some idiot drops the core box and you end up with a pied core you have a good chance of putting it back together again and working out the true depths.
