The Columbia typewriter was invented by a New York watchmaker named Charles Spiro, an man who later became known for the invention of the Bar-Lock typewriter. The Columbia index was one of the earliest examples where differential spacing for letters was used, i.e., rather than the spaces between the letters being the same, the space between each letter in a word depends on which letter had just been typed. Three models of the Columbia were manufactured. The first had upper case only. The second had upper and lower case on two separate type wheels. The third, labelled the "Improved No 2", combined upper and lower case onto one wheel. This third model was the most successful of the three models in the market.