#### Leonardo da Vinci 1452 - 1519

First mechanical calculator may have been conceived by Leonardo da Vinci around 1502.

In 1967 scientists working in the National Library of Spain, Madrid had stumbled upon 2 unknown works of Leonardo da Vinci, now know as the “Codex Madrid”. There was much excitement regarding this discovery and public officials stated that the manuscripts"was misplaced".

In 1968 IBM hired Doctor Roberto Guatelli, a famous world expert of Leonardo da Vinci, to build a replica.

The text beside the replica: “Device for Calculation: An early version of today’s complicated calculator, Leonardo’s mechanism maintains a constant ratio often 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.”