The Controversial Replica
of Leonardo da Vinci's Adding Machine

Prolog: It all started 2 years ago in June 1994 on a trip to Boston. While visiting the "Boston Computer Museum", I bought a booklet named "The History of Computing" by Marguerite Zientara. On page 3 I saw an unusual picture of a calculator titled "Leonardo da Vinci's Calculator". I started asking around about this calculator, but the more I asked, the less I knew, as it is not mentioned in any other book. The calculator became a quest of mine for the last 2 years. It took dozens of emails, faxes, telephone calls and snail mail to gather the information comprising the story of this unusual replica.

Special thanks to Mr. Joseph Mirabella (New York), stepson and assistant to Dr. Guatelli, for his first hand impressions, and the photograph of the Replica.

So, once upon a time ...
On February 13th 1967 an amazing discovery was made by American researchers working in the National Library of Spain, Madrid. They had stumbled upon 2 unknown works of Leonardo da Vinci know as the "Codex Madrid". There was much excitement regarding this discovery and the public officials stated that the manuscripts "weren't lost, but just misplaced".

Dr. Roberto Guatelli was a renowned world expert of Leonardo da Vinci. He specialized in building working replicas of da Vinci. He had built countless such replicas with four assistants, including his chief aid, stepson Joe Mirabella.
Early in 1951 IBM hired Dr. Guatelli to continue building such replicas. They had organized a traveling tour of the machines, which was displayed at schools, offices, labs, museums and galleries.
In 1961 Dr. Guatelli left IBM and set up his own work shop in New York.

In 1967, shortly after the discovery of the "Codex Madrid", Dr. Guatelli flew to the Massachusetts university to examine its copy.When seeing the page with the calculator he remembered seeing a similar drawing in the "Codex Atlanticus".
Putting the two drawings together Dr. Guatelli built the replica later in 1968.

It was displayed in the IBM exhibition.
The text beside the replica said:
Device for Calculation: An early version of today's complicated calculator, Leonardo's mechanism maintains a constant ratio of ten to one in each of its 13 digit-registering wheels. For each complete revolution of the first handle, the unit wheel is turned slightly to register a new digit ranging from zero to nine. Consistent with the ten to one ratio, the tenth revolution of the first handle causes the unit wheel to complete its first revolution and register zero, which in turn drives the decimal wheel from zero to one. Each additional wheel marking hundreds, thousands, etc., operates on the same ratio. Slight refinements were made on Leonardo's original sketch to give the viewer a clearer picture of how each of the 13 wheels can be independently operated and yet maintain the ten to one ratio. Leonardo's sketch shows weights to demonstrate the equability of the machine.

After a year the controversy regarding the replica had grown and an Academic trial was then held at the Massachusetts university in order to ascertain the reliability of the replica.

Amongst others were present Prof. I. Bernard Cohen consultant for the IBM collection and Dr. Bern Dibner a leading Leonardo scholar.

The objectors claimed that Leonardo's drawing was not of a calculator but represented a ratio machine. One revolution of the first shaft would give rise to 10 revolutions of the second shaft and 10 to the power of 13 at the last shaft. Such a machine could not be built due to the enormous amount of friction which would result.

It was said that Dr. Guatelli "had used his own intuition and imagination to go beyond the statements of Leonardo."
The vote was a tie, none the less IBM decided to remove the controversial replica from its display.

Dr. Guatelli passed away on Sep-93 at the age of 89.
The whereabouts of the replica today is unknown. Possibly it is somewhere in one of IBM's storages.
Joseph Mirabella still owns the work shop in New York, with many of the replicas at hand.

Further acknowledgments:
Mr. Javier Susaeta - Madrid, Spain.
Mrs. Maria Cristina Guillén - National Library of Spain.
Mrs. Yvonne Scherzer - RRZN/RVS, University of Hannover, Germany.
Prof. Brian Randell, University of Newcastle, England.
Prof. I.Bernard Cohen , Harvard University, USA.
Dr. F.W. Kistermann - Germany.

"The History of Computing" - Marguerite Zientara.
"Think" magazine - Volume 50 #6, December 1984.
"Codex Madrid I" - Leonardo da Vinci.
"Leonardo da Vinci - Engineer and Architect" - The Montreal Museum of Fine Arts 1987


Codex photo courtesy of RRZN/RVS, University of Hannover, Germany.
Replica photo courtesy of Mr. Joseph Mirabella, New York, USA.


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