eir own defense. It was not even faintly like the ambush of a
cruiser on the bottom of a Kandarian sea, waiting to assassinate a fleet
when its complement went on board. But Bors didn't like what he'd just
done.

The figures wouldn't come out right. Impatiently, he sent for Logan. The
mathematical Talent came into the control room.

"Will you calculate this for me?" Bors asked irritably.

Logan glanced casually at the figures and wrote down the answer.
Instantly. Without thought or reflection. Instantly!

Bors couldn't quite believe it. The distance between the two stars was a
rounded-off number, of course. The relative proper motion of the two
stars had a large plus-or-minus bugger factor. The time-lapse due to
distance had a presumed correction and there was a considerable probable
error in the speed of translation of the ship during overdrive. It was a
moderately complicated equation, and the computation of the probable
error was especially tricky. Bors stared at it, and then stared at
Logan.

"That's the answer to what you have written there," said Logan
condescendingly, "but your figures are off. I've been talking to your
computer men. They've given me the log figures on past overdrive jumps
and the observed errors on arrival. They're systematic. I noticed it at
once."

Bors said, "What?"

"There's a source of consistent error," Logan said patiently. "I found
the values to correct it, then I found the source. It's in your
overdrive speed."

Bors blinked. Speed in overdrive could not be computed exactly. The
approximation was very close--within a fraction of a tenth of one per
cent--but when the distance traveled was light-years the uncertainty
piled up.

"If you use these figures," said Logan complacently--and he scribbled
figures swiftly--"you'll get it really accurate."

Having finished writing the equation, he wrote the solution. Bors asked
suspicious questions. Logan answered absently. He knew nothing about
overdrive. He didn't understand anything but numbers and he didn't know
how he did what he did with them. But he'd worked backward from observed
errors in calculation and found a way to keep them out of the answer.
And he'd done it all in his head. It was unbelievable--yet Bors
believed.

"I'll try your figures," he said. "Thanks."

Logan went proudly away, past an orderly bringing cups of coffee to the
control room. Bors aimed the ship according to the calculation Logan had
given him, scrup