Keuffel Esser 4051 early 52 cm 21″ slide rule 1910 USA

This is a very early extra long slide rule by Keuffel & Esser from New York. It is marked with the patent date of June 5, 1900. Probably produced a little later but still one of the early extra long Mannheim models made in America. It is in great condition and comes with the original case that is was restored using black tape on the far end. It has the original cursor with glass and screws which is also in very good condition but there is a small piece of the glass chipped around 1 screw. The cursor is also marked with a patent number. There are only minimal signs of use and age. It measures 52 cm or 21 inches wide. Check the attached video on how to work your vintage man tool : slide rule operation instructions!