And I wouldn't use Warren Nolan, unless he's updated his formula. His has been the least accurate from what I've seen in the past. I think realtimerpi is a pretty good one.
They were around 9-10 years ago before all these generic pseudo formulas popped up. It is a paysite that non-members can see once a week updates and members can see nightly, if not up to the minute updates.
This may not the true RPI they use but it used to be the only place you could get an RPI. Take that for what its worth.