Founded in 1880 at 109 Deansgate, Manchester by Alexander George Thornton, the firm grew to become one of the largest manufacturers of drawing instruments and slide rules in Britain. The Precision Instrument Co was taken over in 1901 and PIC continued to be used by Thornton as a trade mark until about 1970. The firm became British Thornton in 1967 and merged with ESF at Burley in 1992. Plastic slide rules were introduced ca.1956.

Thornton PIC3648/PC8 ten inch plastic slide rule made for ICS. It has a red cloth covered card case. Scales are: cm\LL2,A{B,C1,C}D,LL3\in//{S,L,T}

Thornton PIC VP114/PC2 closed frame, plastic 5” slide rule. Scales are in\K,A{B,C1,Sd,Td,C}D,L//cm. It has a leather slip case. Date code for 1957.

Thornton PIC VP150PC2A closed frame 5” plastic slide rule. Scales are in\A{B,C1,C}D. It has a red vinyl slip case with B & S Massey Ltd on it. It was a promotional item for them in 1961. It also has its outer retail card box and two instruction leaflets.

Thornton PIC P173 Student’s Log Log closed frame 10” plastic slide rule with metal & glass cursor. Its scales are LL2,A{B,C1,C}D,LL3//{S,L,T}. It has a red cloth covered card case. Made ca.1960.

Thornton PIC P172 Student’s Log Log closed frame 10” plastic slide rule with metal framed cursor, made ca.1960. Its scales are LL2,A{B,C1,SdTd,C}D,LL3. This is the version with the patent differential trig scales. The P173 below is the version with conventional trig scales. It has a red cloth covered card case.

Thornton PIC P171 student’s closed frame 10” plastic slide rule made ca. 1956-60. It has a red cloth covered card case. Scales are: A{B,C}D//{S,L,T}.

Thornton PIC P170 “Junior” closed frame 10” plastic slide rule made ca.1956. Scales are A{B,C}D.

Thornton PIC 67 plastic, closed frame, 5” slide rule. Scales are: A{B,C}D//{S,L,T}. Missing cursor. Ca. 1960.

Thornton No P221 Comprehensive duplex plastic slide rule with plastic cursor. The 27 scales are: LL01,LL02,LL03,DF{CF,C1,ISd,ITd,Td,Sd,C}D,LL3,LL2,LL1//S,ST,T,A{B,L,K,C}D,D1,Ps,Pt. The rule is complete with instructions and black vinyl wallet. Thornton’s most complex rule. Later renumbered AA010.

Two versions of the No 271 Log Log open frame, simplex plastic slide rule. The scales are: LL2,LL3,L,A{B,C1,ISd,ITd,Td,Sd,,C}D,S,ST,T. The upper version is a British Thornton one, post 1967, and is of heavier construction, similar to the P221 above. It has a hard black plastic case. The lower version, dating from 1963, purchased new by me as a student and used throughout my engineering career, originally had a black vinyl wallet. I also have another British Thornton one, like the top one, with a black vinyl wallet.

British Thornton “AD050 Log Log” open frame, simplex, ten inch plastic slide rule. The scales are: LL2,LL3,L,A{B,C1,ISd,ITd,Td,Sd,C)D,S,ST,T. It is complete with its hard plastic case. It is the same as the British Thornton P271, but re-numbered.

British Thornton “AD160 Standard” open frame simplex plastic slide rule. It has a hard black plastic case of the standard British Thornton type. Scales are K,DF{CF,C1,C}D,A. It is the same as the AD060 apart from the deletion of the cm and inch rulers.

British Thornton “AD150 Advanced” open frame simplex, ten inch slide rule made of plastic. The scales are LL1,LL2,LL3,A{B,C1,K,C}D,S,ST,T. It has the usual hard plastic case. This rule replaced the AD050 shown above. On these “Mark 2” rules the differential trig scales had been dropped and this rule has a third log log scale.

British Thornton AD070 (Modern Maths) open frame, simplex, ten inch plastic slide rule. The scales are: K,A{B,C1,C}D,L. It is complete with its hard plastic case.

Thornton PIC No 251 open frame simplex slide rule, which is complete with its black vinyl wallet. The somewhat unusual scales are cms,inches 1/20,DF{CF,C1,C}D,A,inches 1/16. Since there is no bevelled edge and one of the inch scales is not at an edge the cms and inches scales were presumably for conversions and not rulers.

British Thornton No P281 Standard open frame simplex 10” slide rule. It has a hard plastic case. Scales are: cm,K,DF{CF,C1,C}D,A,in. Later renumbered AD060.

British Thornton P241 Log Log duplex plastic slide rule with plastic cursor. Its scales are: LL2.LL3.L.A{B,C1,C}D,S,ST,T//cm,K,DF{CF,C!,C}D,A,in. It has the usual British Thornton black hard plastic case.

British Thornton No AA010 Comprehensive duplex plastic slide rule with plastic cursor. The 27 scales are: LL01,LL02,LL03,DF{CF,C1,ISd,ITd,Td,Sd,C}D,LL3,LL2,LL1//S,ST,T,A{B,L,K,C}D,D1,Ps,Pt. The rule is complete with hard plastic case. This was Thornton’s most complex rule. Originally numbered P221.

British Thornton “AD060 Standard” open frame, simplex, ten inch plastic slide rule. The scales are: cm,K,DF{CF,C1,C}D,A,inch. It has a hard plastic case and instruction booklet ©1971. It is the same as the P281, but renumbered.

Thornton 0552/1448 speed, time, distance slide rule. The scales are the same as the one earlier on this page. It has black PVC covered card snap fastening case.

Thornton VP134-PC5 five inch, closed frame plastic slide rule. A mechanical & electrical engineers’ pocket slide rule, it has a leather slip case. The scales are LL2, LL3, A{B,C1,SdTd,C}D,P with motor/dynamo & volt scales in the well, patent differential scales for monetary calculations at the left hand edge of the stator, and inch and cm rulers. Thornton’s most complex vest pocket rule

Thornton PIC P123/PC18 ten inch plastic slide rule. It has a red cloth covered card case. Scales are: cm\LL2,LL3,A{B,C1,SdTd,C}D,P\in and patent differential monetary scales on the left hand edge of the stator.

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W F Stanley |

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