This is an 1930s Add-O-Matic Calculator in original box with directions in excellent condition.  It was manufactured by Allied Manufacturing Company or Chicago, Illinois in 1937.  Although a small dent on side and some box wear, machine still operates very well.  The seldom found directions pamphlets are also included (One is 6 pages and the other is also 6 pages & both double sided for 12 pages each).  Machine is shown and described in the book “Antique Office Machines” by Thomas Russo.  Machine has slider type keys and a “figures” pointer in which larger figures were used for addition and multiplication and smaller figures used for subtraction.  The secret to operation is to move the slider to desired number, push down the brass button and move slider back.  The results were displayed in the five place window.  Calculator is 5” high x 6” wide x 11” long.  It weighs 6 lbs.  It will be the highlight to computer calculator technology 75+ years ago.