This very rare adder was made in 1901 by the C. E. Locke Mfg. Co. in Kensett, Iowa, U.S.A., and marked as such on the right side.  The left side says The Locke Adder, Patented Dec 24, 1901.   This rare machine is pictured and described in the book “Antique Office Machines” by Thomas Russo.  Invented and patented by C. E. Locke of Wisconsin in December 1901 with Patent Number 689,680.  It was a finger sliding bar type adder with color-coding to readily tell dollars and cents.  There were two models of the Locke adder; one dated 1901 and a second model dated 1905.  Availability is Scarce and value of each is over $ 800.00.   This treasures 10 3/4" long, 4" wide and about 1/2" thick.  There are 9 rows of moveable numbers, and on the left side in the black tin there are marking points that go from 1 cent to 1 million dollars, on the right side the markings delineate units up 100 million.   Internet research shows a portion of provenance notes to show “Its results are always correct, its price within the reach of all. It is a necessity to any up-to-date businessman or accountant. C. E. Locke Mfg. Co., Kensett, Iowa, U.S.A., then shows a picture of a man putting it in his inside coat pocket”.  Note – No instruction book is included, but above provenance notes are accurate.   Calculator is in very good condition with rarely found original green felt backing (1905 and later models had a red felt bottom).   The machine is in very good operating condtion.  This rare treasure will highlight any collection of old calculators.