TREA

with invisibly printed correct answer; the answer being rendered visible by special optical means

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Industry

  • CPC
  • G09B3/045
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Parent Industries

GPHYSICS G09Cryptography, education, displays G09BEDUCATIONAL OR DEMONSTRATION APPLIANCES APPLIANCES FOR TEACHING, OR COMMUNICATING WITH, THE BLIND, DEAF OR MUTE MODELS PLANETARIA GLOBES MAPS DIAGRAMS G09B3/00Manually or mechanically operated teaching appliances working with questions and answers

Current Industry

G09B3/045with invisibly printed correct answer; the answer being rendered visible by special optical means
Industries