What you don't do is go for the 100% accuracy when you already have a failure in the system already.
A US evangelical Christian has predicted that the apocalypse will take place on Saturday, prompting derision from atheist groups. Harold Camping, 89, previously made a failed prediction that Jesus Christ would return to Earth in 1994. But, the head of the Christian radio network Family Stations Inc has said that he is sure an earthquake will hit on May 21, sweeping true believers to heaven and leaving others behind to be engulfed in the world's destruction over a few months. "We know without any shadow of a doubt it is going to happen," he said. Harold Camping, 89, previously made a failed prediction that Jesus Christ would return to Earth in 1994. Camping, a civil engineer who once ran his own construction business, plans to spend May 21 with his wife in Alameda, in northern California, and watch the doomsday unfold on television. "I'll probably try to be very near a TV or a radio or something," he said. "I'll be interested in what's happening on the other side of the world as this begins." Like his last prediction, Camping's doomsday date is based on his reading of the Bible and a timeline dating back to ancient events including the Biblical flood survived by Noah. But atheists are not convinced.
Judging a prophet of the biblical variety is actually fairly straightforward. In the Old Testament we are told in Deuteronomy 18:21-22, "You may say to yourselves, "How can we know when a message has not been spoken by the Lord ?" If what a prophet proclaims in the name of the Lord does not take place or come true, that is a message the Lord has not spoken. That prophet has spoken presumptuously. Do not be afraid of him."
In fact, back then, they stoned false prophets to death (which wasn't a pretty way to go).In otherwords you were either right or you were dead.
Of course these days we don't stone or do anything with false prophets other than mock them for which no doubt loads of internet prophets are very grateful for their ongoing survival.
So as for Mr Camping's prophesy? Well he's already failed the Deuteronomy test, so I expect we'll all be alive tomorrow and right though till the end of the month.
Perhaps he should have stuck to safe things like "a horse will win the Grand national" and stuff like that.