Unlike Thomas's original calculator, of 1820, this enlarged version, with a ten digit capacity instead of six, and provision for addition/multiplication or subtraction/division, is operated by hand. The 1820 model was spring driven.
The most obvious difference between this and the more familiar models of about 1870 and after is its greater size. Not only are the components larger, they are also made to a higher standard, with roller ended detents for the decimal pointer action and for locating the indicator dials. On later models, the bus-bar which moves the gears backwards or forwards for negative or positive calculation is controlled by a simple lever, while the 1848 model has a rotary action activated by the crank on a vertical arbor. When used for calculating, the crank tips on an arbor in the front of the case. On later models, the crank serves for calculating only, and is permanently fixed on a vertical arbor.
Turns of the crank are counted by a screwdrive slide, which has to be set to a number up to 9 before the crank can be turned. Later models have subsidiary indicator digits for each column for the former purpose.
There is no serial number on the machine, which confirms it as a pre-production model, and when exhibited in 1920 was said to be the property of M.A. Darras, the maker of the actual Thomas arithmometre. Another 1848 model was also included in the 1920 exhibition (No 28 in the catalogue) but its present whereabouts is unknown. This, too, was hand-operated.
It is interesting that, although Thomas had produced his first Arithmometre in 1820, and had reached an advanced state of developement by 1848, it was not until the 1870s that full production seems to have started of what was the first successful mechanical calculator to be produced in quantity.