Patent #02190475, assigned Feb 13, 1940 to Fred Gretsch Jr., for the Synchromatic Stairstep Bridge
Patent #02190475, assigned Feb 13, 1940 to Fred Gretsch Jr., for the Synchromatic Stairstep Bridge
Patent #02190475, assigned Feb 13, 1940 to Fred Gretsch Jr., for the Synchromatic Stairstep Bridge
Patent #02190475, assigned Feb 13, 1940 to Fred Gretsch Jr., for the Synchromatic Stairstep Bridge