Exertion Count and Recovery

On PPP4 you have the option of using an exertion count, this is basically a relationship between exercise intensity and duration. According to Polar these exertion count figures can be used to determine recovery periods, as far as I can make out it is about 8 hours recovery for every 100 points. According to Polar this is critical in exercising too early after a training session or training too late after one.
Anyway what I want to know is, is there anybody out there that knows how to calculate recovery from these exertion counts.

Thanks

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