Having some easy to see calibration marks are a tried and tested way of knowing your sail settings at any given time while sailing. It means you can set up the sail to exactly how you you like it from your speed testing pre race and saves valuable seconds at each mark while you are changing each control.
The two most important calibration points are the outhaul and vang as they are slightly harder to set by eye than the cunningham.
For the outhaul, try putting a few wraps of tape around the boom where your outhaul blocks are, I have mine just behind the cleat on the boom so that It’s right in front of me while sailing upwind.
The vang marks should be on the middle primary line of the vang cascade, again wrapping some electrical tape around the rope and using the blocks as a reference point.
Next time you are out pre race, tuning up, take note of what your fast settings are upwind and downwind so you can quickly go back to these settings as you go around the race course!