3499235

Information

• Patent Grant
• 3499235

• References
• Source

• Patent Number

  3,499,235

• Date Filed

  Not available

• Date Issued

  Tuesday, March 10, 1970
  55 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