Probability of God's existence → zero

[Tiberius]

Well, since you put on bold Christianity in my example, let's deal with that. There are 22,000+ Christian denominations. The chances that the one a person believes in is right does drop. Also, we're going to have to reduce the probability of each denominations to an equal level, for a lack of evidence. I'll deal with this more below.

So now you are changing your argument? Your original statement was that the chances that a God is the Christian one is small because there are numerous other Gods. Now you are saying that the chances that a person believes in the correct God are smaller. There is a difference...one deals with the personal choice of a person, the other deals with the actual existence of such beings.

I think we fall short of being able to obtain reliable evidence that an entity exists as God.

That's a separate argument. The point is, you cannot simply make the assertion that all God claims are on an equal level. Certainly there is a way of showing that some Gods are more likely that others. If God A has contradicting attributes, and God B and C do not, then Gods B and C are both more likely than God A.

The problem here is that there is no calculation where "millions of millions of millions" is possible

Erm...yes there is. 1,000,000 x 1,000,000 x 1,000,000. Millions of millions of millions. Otherwise known as a quintillion.

but as some able mathematician I am alarmed you think an infinitesimal amount is "a very actual and measurable amount". In statistics, it is insignificant.

I don't. That was in reference to the "1 in millions of millions of millions", which is an actual and measurable amount.

1) "millions of millions of millions" is synonym for the countless number of entities.

Not really, especially not in statistics. If you want to say "countless" then say it.

2) It is the infinitesimal probability raised to the power of as many definitions we place on God. So, it becomes inconceivably infinitesimal.

Again, based on faulty statistics. You could apply this to anything and say that everything is inconceivable. There are an infinite number of things that could happen when you toss a coin, so the result of a toin coss is inconceivable. Of course, most of those things are infinitesimally small, but two of them (i.e. it landing heads or tails) are very much more probable to occur.