3516177

Information

• Patent Grant
• 3516177

• References
• Source

• Patent Number

  3,516,177

• Date Filed

  Not available

• Date Issued

  Tuesday, June 23, 1970
  54 years ago

• CPC

  • G09B3/085 - with invisibly printed correct answer; the answer being rendered visible by special optical means

• US Classifications

  • 434 - Education and demonstration