Monroe, 1940, L200X, USA
The Monroe Calculating Machine Company was founded by Jay R. Monroe in 1912 in order to make calculators based on the latest design by Frank Baldwin. Baldwin had invented many different calculation machines, but was unable to market them successfully for many years.
The first Monroe calculator was the model A in 1911/1912. Larger scale production started with the model D in 1914. This was followed by the models E, F, and G over the next few years. The model K was released in 1921. Note that it seems that these early model letters simply denote the year it was first made, from A in 1911 to K in 1921.
In 1929 Monroe made the model L, that is mechanically identical to the model K, except that it was about half the size, and much lighter. Versions of the model L/LA were produced until the 1960s. Several further calculator models followed, most of them electrically driven.