Manufactured by Felt & Tarrant Company
Serial number 55544
The Model E Comptometer introduced new features to this line of calcuators, designed to assist operators with error correction. Called the "Controlled-Key", this mechanism was designed to lock the keys in the columns other than the column where the error was detected.
The next, and less successul, feature, were interference guards at the side of the keytops to prevent accidental depression of a key at either side of the one being operated.
The Controlled-Key also prevented any other keystroke from being started until until the up-stroke was completed or corrected.