| Name and Model Number | K&E Sperry Type 3 |
| Country of Origin | USA? |
| Date of Manufacture | c1909 - 1939 |
| Front Scales | ‘S’ scale: L,C,√√ (Square root – 2 circles) |
| Back Scales | ‘L’ scale: 3 circles log scale |
| Scale Length | Approx 12”. |
| Type of Rule | Watch Type |
| Construction | Metal, engraved metal dials |
| Area of Use | Generic |
| Comment | This is the K&E’s “Sperry/Lange” pocket-watch calculator with its very iconic “concentric nuts” winders
which came in a number of versions over about 30 years. K&E continued to use the Model 4017 number through to 1939 with two different US Patent dates on the front face, and also as the Model 4018 for a relatively short time between 1909 and 1927 called the “K&E Calculator” with “Pat Appd. For”. Examples are serial numbered. Please tell us if you have an example and let us have the serial number and type. |
| Rarity | RR |
| Donor | Collection of Peter Hopp |
| Match Number | 49 |
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| RR | = Rare -- 1 of 25 collectors has one; it may take a year to find an example in the marketplace. |
| RRR | = Very rare -- only very few known to collectors; may take several years before one comes up for sale. |
| RRRR | = Extremely rare -- a museum piece; unlikely that an example will ever come up for sale. |