Early typewritten letters are the most solid evidence for the use and proliferations of typewriters. They can also be excellent samples of what the actual product of a certain machine looked like, particularly for index machines with rubber type, that has usually deterioted.

Typewriter factories of course advertised their products in their own letterheads. So, together with original receipts, bills and advertising, they help to piece together the actual history of early writing machines, because patent dates alone are not enough to go by. Some of the information in this online museum is based on exactly such research.