Instructions
Look at the typewriter's back panel. If it says "Wagner Typewriter Co.," it was made between 1895 and 1900 and is a No. 1 or No. 2 model. Because these models are the oldest and only 12,000 were made, they are the most valuable.
Determine if your typewriter has an open or closed frame. If it has an open frame, you'll be able to see the inner workings. If it has a closed frame, the workings will be covered by sheet metal. Open-framed typewriters date from 1900 to the 1930s, while closed-frame models are from the '30s onward.
Look at the rows of keys on your model. Portable typewriters, which were slightly smaller, can be dated by their keys. If your portable model has three rows, it is from 1919 to 1929; if it has four rows, it is from the '30s or '40s.
Check the serial number under the typewriter's carriage. For example, serial numbers 100, 1000 and 10000 are from 1900, 1901 and 1902.