On 10 October 1882, a patent for a simple adding device (US patent Nr. 263904) was granted to Christian W. Hergenroeder of Baltimore (see the nearby image).
The patent model of the device survived to our time and is kept now in the collection of the National Museum of American History in Washington, D.C. (see the image below).
The adding machine of Hergenroeder (he called it a counting machine) has a wooden frame with a round brass top and mechanism, with overall measurements: 5 cm x 31 cm x 21.3 cm.
A ratchet disc under the top has the digits from 0 to 99 indicated on it. The 99 complements also are indicated (for use in subtraction). To the right of the disc is a series of pins labeled from 1 to 10. An arm extending from the right side of the disc fits between the pins. Pulling the arm forward advances the disc by the amount indicated on the scale. When the disc has advanced a full rotation (the sum of the numbers to be added exceeds 100), it advances a smaller, vertically mounted disc on the left side by one unit, for hundreds carrying. Complementary units are also indicated on the edge of this disc.
For convenience in keeping the numbers to be added or subtracted by the operator, is provided a series of nine wooden digit wheels (rollers) having numbers thereon, which rollers are arranged in a recess in the base and partially concealed by overlapping flanges. These are intended for keeping track of numbers used in calculations.
The machine is operated in the following manner: The disk is to be set by turning the same forward by means of the projections k, extending through the case until the numeral 0 is brought to view. Then, supposing the numbers eight, seven, and nine are to be added, the arm C is to be placed in contact with the pin numbered S on the right side thereof, and drawn toward, the operator until the movement is arrested by the lug on the arm coming in contact with the pin. This movement will bring the number 8 to view by the corresponding movement of the disk. Then the arm is to be placed on the right side of the pin numbered 7 and drawn toward the operator in the manner already described, which will cause the disk to rotate until the number 15 appears to view, and in the same manner, when the arm is drawn in contact with pin number 9, the disk will be rotated nine teeth, bringing the number 24, the sum of the three numbers, into view. The operation of subtraction is performed in the same manner, the decreasing series of numbers being observed instead of the increasing series. When the sum of the numbers to be added exceeds one hundred the complete revolution of the disk which represents one hundred will be recorded on the hundreds-wheel by the mechanism above described in that connection. The wheel is to be set so that the first movement thereof will bring the number 1 to view, which number will represent one hundred, and any excess of that number less than a hundred will be read on the disk, the wheel and the disk thus giving the sum total.
Biography of Christian Hergenroeder
The information for Christian William Hergenroeder is very scarce. He was born as Christian Wilhelm Hergenröder in Darmstadt, Germany, in 1863 and emigrated to the USA in 1882, and was naturalized several years later. His wife, Sofia Hergenroeder, was born in August of 1866, also in Germany, and came to the United States in 1891. Their son, Christian Jr., was born in November 1895. Another US patent was granted to Christian Hergenroeder, for an improvement in music leaf turners (US patent Nr. 265602, 1882). He worked as a laborer and clerk and died on 23 October 1906 in Baltimore.