Shoebox Comptometers - Clearing Mechanism

Far and away, the most important concept of the key-driven calculator was the rapid entry of numerical values into the machine. Operators spent 90% of their time actually keying digits which the machine had to quickly and accurately reflect in the register dials. The Comptometer was the first, and for many years, the only machine on the market able to accomplish this task.

(WoodieClearing The need to quickly clear the machine to a zero'd state (sometimes called "cancelling") was of secondary importance since the action was needed only once for each new set of figures to be totaled. While this mechanism was always located on the lower right side of the machine, Felt paid so little attention to the matter that he showed the knob on the left side of the machine in his original patent. An 1888 article in Scientific American describes the action...
"The result of any operation being obtained, the machine is returned to naught by depressing the lever which appears on the right and turning the knob above it until the figures seven appear on the register, when release the lever and continue turning the knob, and the machine will stop at the ciphers."

(Clearing-B The first metal cased models in early 1904 provided an improved mechanism requiring much less manipulation by the operator. Clearing was now accomplished with a rather deliberate backward movement of the handle and another deliberate return movement to the resting postion.

Over the years before 1920, F&T new designs (models A- thru F-) would include only incremental improvements to this mechanism, some to decrease the effort required, others to reduce the noise generated, etc. However, F&T's competitors were to provide a superior clearing operation much earlier..

(Clearing-MA True ease of cancelling first comes into view as early as 1902 on the Mechanical Accountant, a machine that would never gain significant market share dispite some innovative technology. According to McCarthy "A clearing lever having a stroke of about one-quarter inch, clears all totals simultaneously." Also, the machine had a large lateral "thumb-bar" that cleared the "item register", unique on the machine for its time.

(Clearing-BU A more serious threat came when the Burroughs key-driven calculator appeared in 1911. Their look-alike calculator located the clearing handle on the right at mid-keyboard where only a single forward pull was required. The spring-loaded handle would then return on its own to the resting position. All in all, much superior to the Comptometers then on the market.

At this time, the design talents of both Felt and Turck were focused on getting the "Controlled Key" feature into production, a formidable undertaking.

(Clearing-H1 It was not until 1920, with the appearance of the H model that the Comptometer would provide a truly competative clearing function with a simple, easily operated, lightweight action. The clearing action would be unchanged for the J-model that appeared six years later.

When electric-driven machines arrived, clearing would be motorized and no longer present the difficulties encountered previously.

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