Aaron Hatfield – Complete Biography, History, and Inventions

Hatfield's machine for adding numbers

Aaron Hatfield – Complete Biography, History, and Inventions

Key Points

  • Aaron Hatfield was an American inventor and watchmaker who was born in Pennsylvania in 1819.
  • Aaron Hatfield was most famous for his disc-shaped adding machine. He also invented several other devices, including pruning shears and a bag holder.
  • Aaron Hatfield married, had two children, and died in 1898.

Who is Aaron Hatfield?

Aaron Hatfield was a watchmaker and inventor, most famously known for the Hatfield adder. The Hatfield adder was a circular adding device made from three concentric brass discs and a lever set on a wooden paddle. Hatfield also took three US patents on pruning shears, pumps, and an improvement on bag holders in his lifetime, depicting his ability to dabble with different trades with varying success.

Early Life

Little is known about his early life, but Aaron was born in Pennsylvania in 1819.

Quick Facts

Full Name
Aaron L. Hatfield
Net Worth
Place of Birth
Fields of Expertise
Adding machine


The 1850 US Census details him as a watchmaker, though he added a few skills over the years. In the 1860 US Census, Hatfield moved to Sandusky, Ohio, and worked as a photographer (ambrotypist). The inventor died in December 1898 in Three Rivers, Michigan, where he had a jewelry and musical instruments store. Hatfield spent the last year of his life secluded above the store.

What Did Aaron Hatfield Invent? What is He Known For?

Hatfield is known for three patents, but the adding machine is the most popular. It had a number of metallic disks with numbers stamped and set with springs. The adding machine is placed on a base plate made of mahogany shaped like a mirror. It also has a hole where it is possible to hang the machine. It is capable of adding numbers from one to 9,999. The highest that can be added in one operation via the device is 99, though.

Hatfield’s machine for adding numbers (© Jay Goldman, https://www.jmgoldman.com)

The calculator of Hatfield was made with wood (mahogany), iron, and brass, with dimensions 2.5 cm x 24.5 cm x 14.5 cm. It was an adder and consisted of a series of circular metallic disks having numbers stamped thereon, so arranged, in connection with springs, that by the alternative movement of a lever, any number of figures, from one to 10,0000 or more, could be correctly and easily added together.

The adder has an engraving titled “A. L. HATFIELD INVENTOR AND MANUFACTURER LEVISBURG PA.” Its serial number is 399, and the wooden frame measures 9-5/8.

Aaron Hatfield also took three other patents, including №103327 in 1870 to improve pruning shears. Another patent was initiated in 1873 to modify pumps detailed №143759. At this time, Hatfield was living in Clyde, Ohio. The final patent listed №199705 was for a bag holder modification in 1878. 

The patent drawing of Hatfield’s Adder.

The adding device is mounted on a mahogany base plate in the shape of a handheld mirror. There is a hole at the end of the handle for hanging the machine.

The calculating mechanism consists of three, concentric brass discs of different diameters, that are mounted on top of each other and to the mirror portion of the mahogany base.

The largest disc is fixed to the mahogany base, and it has the numbers from 1 to 99 indicated around the edge (there also is a blank space for zero). The middle and upper discs rotate about a central pivot, which has a smaller pin attached to it that holds the discs together. The middle disc is divided into 100 parts around the edge, with the parts numbered from 100 to 9900 (again there is a blank division). The top disc has the numbers from 1 to 99 around the edge, as well as a blank. Next to each digit of the disc, there is a small sunken tooth in the disc. A hole in the arm allows one to see numbers on the discs.

To use the instrument, the operator sets up thousands by rotating the middle disc. There is an iron handle at the very end of a crossbar (attached to the common center of the discs), with which the operator rotates the bar. To add one or two-digit numbers, the operator moves the arm counterclockwise so that it is over the desired number on the outer rim. Then, rotating clockwise back to zero, a spring ratchet attached to the arm engages a tooth on the inner disc and rotates it through the number setup. When the inner disc goes a full revolution, a carry mechanism advances the middle wheel one unit.

There is also a thin iron bar coming off of the side of the crossbar. The other end of this bar fits in the engraved wedge-shaped grooves around the inner circumference of the topmost brass disc. This bar permits the crossbar to be rotated only counterclockwise.

Hatfield’s adder, closer view (© Jay Goldman, https://www.jmgoldman.com)

Aaron Hatfield: Marriage, Divorce, Children, and Personal Life


Hatfield was married to one Ida A. Hatfield, born in 1827. There is no family listed for the 1860 US census, though. Hatfield apparently lost his wife and was listed as widowed by the 1880 US Census. He was then living in Constantine, St Joseph County, Michigan.


Hatfield had two children with his wife but there is limited information following the 1850 Census. They were not listed in the 1860 or subsequent Censuses indicating the children may have perished.


Hatfield was widowed though there are limited details on his wife’s death or the whereabouts of his children.


Frequently Asked Questions

Who was Aaron Hatfield?

Aaron Hatfield was a 19th-century inventor, watchmaker, and photographer who is known for four US patents on various items.

What did Aaron Hatfield invent?

The most popular patent is for an adding device known as Hatfield’s Adder. Hatfield put the adding machine in production for several years, and a few devices have since survived to the present. He also took out three other patents. These include a few modifications to pruning shears, bag holders, and pumps.

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