Chuckanut
Give me a museum and I'll fill it. (Picasso) Give me a forum ...
Firecalc doesn't tell you the exact point at which your portfolio will survive or not. It only tells what would have happened historically. In other words, it's a tool for rough estimation. No tool can be anything else when dealing with something as unpredictable as equity prices.
+1
The idea that a 100% success rate is some type of guarantee is bogus. It just tells you what would have happened.
IMHO, tools like Firecalc, when used with conservative numbers, are a good reason for sleeping well at night. But, it's not a good reason for assuming 100% guaranteed, safe, sure, bullet proof retirement funding for the next 30-40 years. Nothing can guarantee that.