I think it is the same calculation method as can be found in Grim Tales (which I do not have), but it was originally devised by Upper_Krust (he posts on these boards) and is available for free as a PDF. If you want a copy I can send it to you by e-mail. The calculation method presented there treats ECL and CR as one and the same (I am not sure what the logic is behind that - it is not justified in the PDF). I simply think that Regeneration 1 (and that's with no vulnerabilities to bypass it - with vulnerabilities it is stated as even less than that) is worth significantly more than 0.2 ECL that is stated in the calculation method - it allows the PC to completely recover after every battle! Fast healing is stated in the same calculation method to be worth even less - only 0.075 ECL!
This seems to be the most widely used ECL calculation method found on these boards, but I don't trust it fully. I am not good at balancing (I keep on saying this...), but some of the numbers presented therein simply sound way off to me.