it with the power deck."

"Well--I mean--what specifically?" asked Tom softly.

"For instance, I've got to find the ratio for compression on the main
firing tubes, using a given amount of fuel, heading for a given
destination, and taking a given time for the passage."

"But that's control-deck operations--as well as astrogation and power!"
exclaimed Tom.

"Yeah--I know," answered Astro, "but I've still got to be able to do it.
If anything happened to you two guys and I didn't know how to get you
home, then what?"

Tom hesitated. Astro was right. Each member of the unit had to depend on
the other in any emergency. And if one of them failed...? Tom saw why
the ground manuals were so important now.

"Look," offered Tom. "Suppose we go over the whole thing again together.
Maybe you're fouled up on the basic concept."

Tom grabbed a chair, hitched it close to the desk and pulled Astro down
beside him. He opened the book and began studying the problem.

"Now look--you have twenty-two tons of fuel--and considering the
position of your ship in space--"

As the two boys, their shoulders hunched over the table, began reviewing
the table of ratios, across the quadrangle in the examination hall
Roger Manning stood in a replica of a rocket ship's radar bridge and
faced Captain Strong.

"Cadet Manning reporting for manual examination, sir." Roger brought up
his arm in a crisp salute to Captain Strong, who returned it casually.

"Stand easy, Manning," replied Strong. "Do you recognize this room?"

"Yes, sir. It's a mock-up of a radar bridge."

"A workable mock-up, cadet!" Strong was vaguely irritated by Roger's
nonchalance in accepting a situation that Tom had marveled at. "You will
take your manuals here!"

"Yes, sir."

"On these tests you will be timed for both efficiency and speed and
you'll use all the tables, charts and astrogation equipment that you'd
find in a spaceship. Your problems are purely mathematical. There are no
decisions to make. Just use your head."

Strong handed Roger several sheets of paper containing written problems.
Roger shuffled them around in his fingers, giving each a quick glance.

"You may begin any time you are ready, Manning," said Strong.

"I'm ready now, sir," replied Roger calmly. He turned to the swivel
chair located between the huge communications board, the adjustable
chart table and the astrogation prism. Directly in front of him was the
huge radar scanner, and to one side