The scoring system rewards charts which best resemble the racing results. It looks at each crew in turn and calculates the total area on the chart between your predicted chart lines and the actual results. (Each day is 1 unit wide and each crew is 1 unit high.) These 'Error Area' scores are then added together - and in essence the lowest score wins. The actual numbers are rejigged into a kind of percentage score. 0 is scored if you did not predict any bumps at all. 100 is scored if you predict everything exactly right. Negative scores are likely - knowing the Bumps!
In addition, each score includes special bonuses, awarded for correctly guessing which crews finish Head of each division at the end of racing. A bonus of 3 points is awarded for each division's head crew guessed correctly. The scaling of the 'error area' component is adjusted so that 100 is the overall maximum score. i.e. If there are 2 divisions being scored, then the maximum score of the 'error area' is 94.
Each division is scored separately. For the four day competition your overall score is calculated as an average of your best two divisions. You therefore have to predict at least two divisions to be entered. For the daily competition, you have to predict at least three divisions to be entered and your best three scores count. You can predict more divisions than this; those that score lowest are simply ignored for your final score!
When the score for a division is being calculated, any 'error area' lying within the division is counted - including for those crews moving into or out of the division.