The Comptometer Model F adding machine, made by Felt & Tarrant, from around 1917.
This is episode 11 of my video series about calculating devices.
"Methods of operating the Comptometer" PDF: https://faculty.fairfield.edu/cstaecker/files/machines/methods_comptometer.pdf
End song inspired by "Hotter Than a Molotov" by The Coup.
Chris Staecker webarea: https://faculty.fairfield.edu/cstaecker/