¶ A teacher hands her pupils stiff cards covered with numbered squares. She gives them a "choose-the-correct-answer" test in which they are to check the proper numbers. The test over, the teacher runs the cards through what looks like an adding machine. The cards emerge with a red mark in every proper square. Krexit enables teacher and pupils to see mistakes at a glance.
¶ A teacher goes through the classroom with a Sight Meter in her hand. Its quivering needle shows in footcandles the amount of light in the room. If in any...
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