Accession No

3010

Brief Description

slide rule to adjust gun elevation for anti-aircraft use, attributed to J. H. Steward, English, 1/2 20th Century

Origin

England; London [based on attributed maker]

Maker

J. H. Steward [attributed]

Class

calculating; military

Earliest Date

1900

Latest Date

1950

Inscription Date

Material

plastic (celluloid?); metal (steel, brass)

Dimensions

length 166mm; width 54mm

Special Collection

Steward collection

Provenance

Collection purchased from member of the Steward family, 1974.

Inscription

Description Notes

White plastic slide rule, held together with screws, for adjusting gun elevation for anti-aircraft use.
Obverse: upper part of stock has scale for ‘height of range in aeroplane in feet’, divided 2000 - 10000, numbered by 1000. Slide has scale of ‘angle of sight to aeroplane’, divided 7˚ - 45˚, numbered 7, 8...20, 25...45, 7 - 20 subdivided to 30´, 20 - 45 subdivided to 1˚; slide also has an arrow pointing to upper scale. Lower part of stock has scale of ‘range in yards to target’, divided 1000 - 10000, numbered by 1000, 1000 - 5000 subdivided to 100, remainder subdivided to 500.
Reverse: map scale for 1:100000, divided [0] - 1200 yards, numbered by 1000, subdivided to 100. Map scale for 1:40000, divided 0 - 6000 yards, numbered by 1000, subdivided to 100. Table for calculating distances in yards from the angle of sight. Also formula for angle of sight, range and difference in height.

Condition fair (very discoloured, corrosion of screws); 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.

FM:42293