We give points for each minute your are in each zone, then that is divided by 60 to give your per second to give you your score.
For example: If you are in the Yellow zone for a minute you would be allocated 15 points, your leaderboard will show 15/60 per second, so .25 per second, to add up to 15 for that minute, if you drop below within that minute you will get the point value associated with that heart rate level.
5 points per minute for Light Green
10 points per minute for Green
15 points per minute for Yellow
20 points per minute for Orange
0 for Red.
Below is a chart with the zone values.