Accession No
5962
Brief Description
"Junior Calculator" and circular slide rule, by Fowler's (Calculators) Ltd., English, 1950 (c)
Origin
England
Maker
Fowler's (Calculators) Ltd.
Class
calculating
Earliest Date
1950
Latest Date
1960
Inscription Date
1896
Material
metal (aluminium); plastic (acrylic?, vinyl?); paper (card)
Dimensions
dial diameter 113 mm; depth 4 mm case length 120 mm; width 122 mm
Special Collection
Brian Harland collection
Provenance
Donated on or before 16/07/2003.
Inscription
'THE
FOWLER
CIRCULAR SLIDE RULE' (card dial on slide rule side of object)
'FOWLER'S
JUNIOR CALCULATOR
Established 1896 Made in England.
FOWLER'S (CALCULATORS) LTD. SALE.' (card dial on calculator side of object)
'THE
Fowler
"JUNIOR"
CALCULATOR
& CIRCULAR
SLIDE RULE ' (On case)
Description Notes
"Junior Calculator" and circular slide rule by Fowler; c. 1950
Aluminium circular outer ring, with large double-sided card dial showing calculator scales on one side and slide rule scales on the reverse. Smaller transparent plastic dial attached over card dial, with rotating black hairline on both sides. Transparent plastic cover with red hairline on calculator side, fixed relative to the metal case.
Calculator scales include: multiply, reciprocal, sines, tans, conversion scales to/from miles/km, Sq.mtrs/sq. yds, mtrs/yds, lbs/Kg, cm/ins
Slide rule scales: radian, EHP, log e10, pi/4, square root 3, sqr roots, sines, tans.
The number of significant digits on slide rules was proportional to the size of the rule (and the smallest graduations that a typical person could resolve.) By wrapping the scales around a circle, the manufacturer could increase the scale length while keeping the overall length modest.
Brown vinyl (?) case printed 'The Fowler "Junior" Calculator & Circular Slide Rule' in gold. Print a little worn.
Conditon good; complete
References
Events
Description
Developed during the seventeenth century, the modern slide rule is based upon the design by William Oughtred (circa 1630). It is one of many calculation devices that is based on the logarithmic scale, a calculation method invented in 1614 by John Napier.
Before the rise of the pocket electronic calculator in the 1970s, the slide rule was the most common tool for calculation used in science and engineering. It was used for multiplication and division, and in some cases also for ‘scientific’ functions like trigonometry, roots and logs, but not usually for addition and subtraction.
A logarithm transforms the operations of multiplication and division to addition and subtraction according to the rules log(xy) = log(x) + log(y) and log(x/y) = log(x) - log(y). The slide rule places movable logarithmic scales side by side so that the logarithms of two numbers can be easily added or subtracted from one another. This much simplifies the alternative process of looking up logs in a table, thus greatly simplifying otherwise challenging multiplications and divisions. To multiply, for example, you place the start of the second scale at the log of the first number you are multiplying, then find the log of the second number you are multiplying on the second scale, and see what number it is next to on the first scale.
Circular slide rules allow the longest dimension to be reduced by a factor of about 3 (i.e. π).
FM:46425
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