BASIC DESCRIPTION Antique Addometer portable mechanical adding machine #2 by Reliable Typewriter & Adding Machine Company, Chicago, Illinois. Stylus-operated dial adder, vintage calculator, antique office machine, 1927–1950s hard-shell leatherette case with green velvet interior. Fully functional, cleaned and oiled. Original documentation set included: yellow Directions & Explanatory Diagram fold-out and "Stop Making Mistakes in Figuring — Use Addometer" promotional brochure, Marmic Sales Co., Brooklyn NY.
FULL DESCRIPTION
Every Addometer that survived did so because someone kept it. This one kept its papers too.
What You Are Getting
A fully functional antique Addometer portable mechanical adding machine by the Reliable Typewriter & Adding Machine Company of Chicago, Illinois, in its original hard-shell leatherette case with green velvet interior. Stylus included. This unit comes with a distinct and charming original documentation set:
Two original period documents. Two different angles on the same machine — one telling you how to use it, one trying to sell it to someone else. Both survived.
A Note on the Case
This unit's case features a green velvet interior, a variation from the more commonly seen purple — a detail that speaks to the production range across Reliable's manufacturing run at 303 West Monroe Street, Chicago: 1927 through the late 1950s. Hard-shell leatherette exterior with embossed ADDOMETER ADDING MACHINE stamp on lid and twin snap button closures. This is the premium case variant, distinct from the later cardboard-box editions.
How It Works
The Addometer is a stylus-operated mechanical adding machine — a dial adder — introduced in 1927 by the Reliable Typewriter & Adding Machine Company of Chicago. Insert the stylus beside a large inner digit and rotate clockwise to add. Use the small outer digits and rotate counter-clockwise to subtract. Results accumulate in the windows. Pull the zero lever to clear. No batteries, no electricity — precision mechanical arithmetic that has worked for a century and will work for another.
From the STEMpunkED Collection
This piece comes from STEMpunkED, a hands-on educational initiative dedicated to teaching science and computation through the actual instruments of history. More pieces from the STEMpunkED collection will be listed over time. Please see other listings.
CONDITION Fully functional — all dials, clearing lever, and stylus confirmed working after individual cleaning and oiling. Original hard-shell leatherette case with green velvet interior and twin snap button closures intact, showing honest age-appropriate wear consistent with a 1927–1950s production instrument. Original documentation present with age toning and edge wear on the Directions sheet consistent with decades of storage; promotional brochure intact.
Returns: 30 days. Buyer pays return shipping. Shipping: Buyer pays shipping and insurance.