When prospecting, what is the percentage likelihood of a "Decent" reading meaning there will be ore?

Is there any documentation on what likelyhood readings mean in terms of percentages?

So would a decent reading be 40%, 50%? More? Less?

I've had luck funding ore in basically every level of prospecting likelyhood, so just wondering if it's really worth chasing an ultra high rating?

A chart with corolating values would be a godsend