Alexander George Thornton founded his business in 1880 in Manchester, took over the Precision Instrument Co in 1901 and in 1967 changed the name of the company to British Thornton. The firm grew to become one of the largest manufacturers of drawing instruments and slide rules in Britain. PIC continued to be used by Thornton as a trade mark until about 1970. The plastic slide rules were introduced in the 1960s. British Thornton merged with ESF at Burley in 1992 and is now a manufacturer of school furniture in Keighley. (History sourced from here).
I acquired two models, one from a car boot sale (AD 070 below), the other (ADO 050) from a house clearance.
The slide rules scales on AD 070
Scales C and D are used for multiplication and division
Scales A and B are used for squares and square roots
Scale K is used for cube roots
Scale L is a logarithmic scale and provided logarithms to base 10
CI is a reciprocal scale
The slide rules scales on AD 050
The model has the same scales as above (apart from scale K) with the following additions:
Scale LL2 and LL3 are log-log scales, used for calculating powers and exponentials
S, T, and ST scales are trigonometric scales used to determine the sine and tangent of angles
Examples of Types of Model produced by British Thornton include
- AA010: A comprehensive slide rule designed for engineering and surveying
- AD 150: An advanced slide rule
- P281: A standard slide rule
- AD 050: A log maths slide rule
- AD 070: Modern maths
- P221: A duplex slide rule that has both standard type and differential trig scales
A user manual covering the range of British Thornton slide rules can be downloaded here.
Sources of Information
The Sources of information below provide comprehensive coverage of the types of slide rule produced by the company (and others) which does not justify repeating here.
British Thornton Slide Rule – BBC A History of the World
British Thornton – Slide Rule Museum – founded in 2003 in USA, The ‘International Slide Rule Museum’ contains many personal accounts of users of slide rules
Tina’s British Thornton Rules – another comprehensive source of slide rules in general
A G Thornton – Mathematical Instruments – considerable detail of the construction and scales used.