This picture from a 1941 printing of a Monroe brochure shows the L 160-X calculator's small size - it even came with its own carrying case.
This specimen lost its carrying case, but otherwise has survived very well. A Monroe L 160-X (Executive) mechanical calculator. As the advertising text of the brochure notes; it really is amazingly compact, the main body measuring only 15 by 22 cm. (I.e. tiny compared to calculators of the time.)
This type was introduced in 1929, basically a half-sized version of their earlier machines. Around 1936 the pale green keyboard was introduced with the extra shadow-mask plate for better visibility of pressed-down keys. Probably around 1939 the handles were given a more modern, straight shape. This specimen still has the crackle-pattern black on green paint on the main body and the old style Monroe logo - by the late 1940s this was changed to a script logo and a plain finish.
As is noted by others, it's very light-running and quiet compared to other calculators, e.g. pinwheel machines. In some company advertising it was actually referred to as the Monroe Noiseless.
This particular specimen was originally purchased new by a building firm in Munich, where it was used in their office. With the advent of electronic calculators, the machine was put away with others in a storage room - and likely forgotten about. The son of the founder of the firm remembered seeing it being used when he was a child in the 1950s. He was now clearing out the old offices, found it again, and put it up for sale online. And there it was purchased by its second owner (me).
The Typewriterdatabase is also a great resource for calculators!; the serial-number resources of The Database (Nomda) confirmed that this calculator was made in 1946. This matches the start of the firm - who started doing work for the Americans also at that time. Buying an American calculator too - it fits.
It needed cleaning, some minor repairs and only small cosmetic touch-ups - repairs well worthwhile for this very nice and working calculator.
The calculator had evidently been used with care and stored well; a light wipe with a damp cloth was really all that was needed. Even on generally clean machines however, the keys accumulate dirt and 'gunk'. To properly clean that and stabilize any cracks in the plastic, the keytops were taken off. Many keys simply pulled off, the remaining keys were pried off with (curved) pliers resting on a strip of rubber for support to not damage the paint.