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. British Thornton is now a manufacturer of school furniture in Keighley.
Thornton PIC Junior closed frame slide rule made of plastic faced mahogany with a metal and celluloid cursor. The scales are: A{B,C}D//{S,L,T}. It has a black card case.
Thornton 6039½ mahogany and celluloid, ten inch, closed frame slide rule complete with case which has a wooden inner sleeve and card outer covered with imitation fish skin. Scales are in\A{B,C}D\cm//(S,L,T}. The rule has a list of Thornton slide rules and details of two slide rule books on the reverse. In the well there is “DRGM 164885” which is Nestler’s registered design for nickel-silver screws holding on the celluloid facings so the rule was presumably made for Thornton by Nestler. It is fitted with a special cursor with a pointer which points to the inches scale, which is specially divided to fiftieths for use in evaluating engine indicator diagrams. Catalogued in 1916 as Thornton’s “Improved Standard Pattern Slide Rule”.
Thornton PIC Junior closed frame slide rule made of plastic faced mahogany with a metal and celluloid cursor. The scales are: A{B,C}D. It has a black card case. Basically the same as the one above but without scales on the back of the slide and the cutouts in the back of the stock for reading those scales.
Thornton PIC New Electrical and Mechanical Engineer’s Rule. 10” celluloid faced mahogany slide rule dated 1931 in a green cloth covered, card box. Scales are cm\LL2,LL3,A{B,C1,C}D,K\in//{S,L,T} and dynamo/motor, volt in the well. This model was first catalogued in 1930. It is complete with a June 1930 edition instruction booklet with a pasted in note and appendix covering the new scale arrangement including the two Log Log scales dated June 1931. The back is plain white celluloid faced.
Thornton PIC No 131 engineer’s slide rule, made of mahogany, faced with plastic. It is of closed frame construction. The scales are: LL2,LL3,A{B,C1,SD,TD,C}D,K//dynamo, volt (in well). There are inch and centimetre rules on the top and bottom edges. This rule has both the single line cursor and the optional three line cursor. There are tables on the back. Date code '49'.
Thornton PIC No F3654 / PC8 closed frame slide rule made of plastic faced mahogany with a metal and glass cursor. The scales are: A{B,C1,C}D//{S,L,T}. There are inch and centimetre rules on the top and bottom edges. It has a red card case. Date code ‘11.61’
Thornton PIC VP114/PC1 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 No 121/PC18 closed frame ten inch mahogany and celluloid slide rule, date coded 11/59. The scales are cm\LL2,LL3,A{B,C1,Sd,Td,C}D,P\in. There are tables on the back. It has a red card case.
Thornton No P221 Comprehensive duplex plastic slide rule with plastic cursor. The 25 scales are: LL01,LL02,LL03,DF{CF,C1,SD,TD,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. This was 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,SD,TD,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.
British Thornton “AD050 Log Log” open frame, simplex, ten inch plastic slide rule. The scales are: LL2,LL3,L,A{B,C1,Sd,Td,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.
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.
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.
Thornton PIC No. 101/PC8 closed frame 10” mahogany & celluloid slide rule with metal & glass cursor. Its scales are: cm\A{B,RC,Sd,Td,C}D,L\in. It has a red cloth covered, card case. Date code 8/60. Originally the property of the UK Atomic Energy Authority (stamped on the reverse of the slide).
Thornton PIC No 111/PC8 closed frame 10” mahogany & celluloid slide rule with metal & glass cursor. Its scales are cm/F,A{B,RC,SdTd,C}D,L\in. It has a fawn cloth covered, card case. F and RC are Thornton names for the K and C1 scales. The tables on the reverse are the same as on the 101/PC8.
Thornton PIC No 101 ten inch celluloid faced mahogany slide rule with metal & glass cursor. It has a green cloth covered card case. Scales are: cm\A{B,R,SdTd,C}D,L\in. Date code 10/56. This is a much wider rule than the No 101 above but is not quite as wide as the No 101/PC8 below.
Thornton PIC No 112/PC9 closed frame 20” mahogany & celluloid slide rule with metal & glass cursor. Its scales are cm/F,A{B,RC,SdTd,C}D,L\in. It has a red cloth covered, card case. F and RC are Thornton names for the K and C1 scales. There are tables on the reverse,. This is the large size version of the no. 111 above
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 Rule Slide RA 10” VF1766. Mahogany and celluloid closed frame slide rule with two metal framed cursors and trig formulae on the reverse. Scales are: in\A{B,C}D\cm//{S,ST,T}. It was normal for British artillery slide rules to have two cursors. It has a green cloth covered card case of the usual Thornton type for this period.. Date code ‘50’.
Thornton PIC No 101 closed frame slide rule made of plastic faced mahogany with a metal and glass cursor. The scales are: A{B,SD,TD,C}D,L. There are inch and centimetre rules on the top and bottom edges. It has a green card case. There are tables on the back. Date code ‘45’.
Thornton PIC No 111 closed frame slide rule made of plastic faced mahogany with a metal and glass cursor. The scales are: L,A{B,C1,Sd,Td,C}D,K. There are inch and centimetre rules on the top and bottom edges. It has a green cloth covered card case. There are tables on the back. Date code ‘C46’.
Thornton PIC 10” closed frame mahogany & celluloid slide rule with green leatherette covered case. PC6A cursor. The scales are: cm\A{B,C1,C}D\in//{S,L,T}. Dated 1938.
Thornton PIC No 121 closed frame slide rule made of plastic faced mahogany with a metal and glass cursor. The scales are: cm\LL2,LL3,A{B,C1,SdTd,C}D,K\in. It has a green cloth covered card case. Made in 1943, the 3 line cursor is a later replacement of the PC8 type.
PIC No 3649 log log ten inch mahogany and celluloid slide rule. Metal framed cursor. Scales are: cm\LL2,A{B,C1.C}D,LL3\in//{S,L,T}. Date code 50 for 1950. It has a green cloth covered card case.
Thornton PIC 144 AC Electrical ten inch mahogany & celluloid slide rule with magnifier fitted cursor. It has a leather case. Scales are: in\sin,cos,A{B,C1,Z,centigrade,fahrenheit,C}D,T\angle,L//{LL1,LL2,LL3,L). Date code 9/55.
Thornton PIC Log Log 10” slide rule of the Perry type dated 1933. The mahogany and celluloid slide rule has a metal & glass PC7a cursor. It has a green, cloth covered card case. The scales are: cm\LL2,A{B,C}D,LL3\in//{S,L,T}.
Thornton PIC Electrical and Mechanical Engineer’s Rule. 10” celluloid faced mahogany slide rule dated 1931 in a green cloth covered, card box. Scales are cm\LL2,A{B,C}D,LL3\in//{S,L,T} and dynamo/motor, volt in the well. The tables on the reverse are the same as those on the rules below.
British Thornton No AA010 Comprehensive duplex plastic slide rule with plastic cursor. The 25 scales are: LL01,LL02,LL03,DF{CF,C1,SD,TD,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.