The 'Paragon' was Keystone's first patented stereoscope.
Keystone View Company of Meadville, Pa., was the world's largest producer of stereographs and was in business from 1892 to 1970 on a limited basis. The company was founded by Benneville L. Singley who at one time worked for Underwood. Singley photographed many of the views sold by Keystone. Keystone would eventually purchase almost all of their competitors. The remains of the Keystone Company are housed at the University of California. Singley filed for 2 patents for stereoscopes, the first in 1898, about the time Keystone started producing them. C. L. Pappenhagen, an employee of the company filed for 4 patents for a total of 6 for the company. Here are some examples of the many forms of hand held stereoscopes produced by Keystone. (http://home.centurytel.net/s3dcor/Keystone/Keystone.htm)
Timber stereoscope reader with brass fittings, used for viewing stereoscopes (Stereoscope cards contain two separate images printed side-by-side to create three-dimensional illusion)