"Some of the time," Norty agreed. "When you are right, you are the sharpest PC this lab has ever tested. But that's only a rather small part of the time. When you're wrong, you're really wrong."
"So he may not die!" I said. "What did I tell you?"
"Show me!" she demanded.
"All right," Norty said. "Take a look at this. You remember giving me all those predictions about temperature and barometric pressures?"
"Yes," she said.
"We've drawn a couple moving weather maps," Norty explained. "Just the pressures on these. They cover the thirty-day period for which you PC'd. One of the maps shows the actual isobars as they were recorded by the Weather Bureau. The other moving map is the same isobars as predicted by you, Pheola. We'll run the two maps simultaneously on a screen. The black lines are the actual readings. The red lines are your predictions."
It was sort of like watching an animated cartoon. The map started with an overlap of red and black and then you could see each high and low pressure area work its way across the country and out to sea. But there was a difference. After a couple hours, on their time scale, Pheola's map differed from the actual, and the difference grew greater for a while, and then narrowed. Suddenly the red and black lines were identical.
The cycle repeated several times in the thirty-day period.
"What you see," said Norty, "is that she is right for a few hours and then wanders off, sometimes for several days, but wanders back and gets right again. The timing of when she is right is rather random—there's no regular periodicity to it, and as a result, we can't see how to predict when she is going to be right and when she is not."
"I have a thought for you," I said, when Norty had shut off the projection. "It's sort of like two sine waves that intersect now and then. One of them has bigger amplitude than the other, or their periodicity is different. Can't you feed this dope to your computers and find out what kinds of curves would represent the coincidences?"