That's terrific. I love sites like that. They're trying to create a pseudo-scientific approach to the end times. Funny stuff.
It resembles the Saffir-Simpson scale for hurricanes, but it only goes to category 4:
Rapture Index of 85 and Below: Slow prophetic activity
Rapture Index of 85 to 110: Moderate prophetic activity
Rapture Index of 110 to 145: Heavy prophetic activity
Rapture Index above 145: Fasten your seat belts
Since the current index is 159, they need a category 5...