Note
Radio's Master Catalog, copyright 1937, p. F-19.
Radio Craft, May 1937, inside front cover.
Radio Craft, Jun 1937, inside front cover. (looks different than in May)
The "senior" oscilloscope, as opposed to the model 530 "junior" version.
References
Technical description. Radio Craft, Aug 1937, p. 79.
Brief description. Radio News, Sep 1937, p. 139.