1621991

Information

• Patent Grant
• 1621991

• References
• Source

• Patent Number

  1,621,991

• Date Filed

  Not available

• Date Issued

  Tuesday, March 22, 1927
  97 years ago

• CPC

  • G01J1/14 - using comparison with a surface of graded brightness

• US Classifications

  • 396 - Photography
  • 033 - Geometrical instruments
  • 356 - Optics: measuring and testing