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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  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”.
A G Thornton ‘Routledge’ engineer’s slide rule dating from the late 19th century. The inner faces are normal 2 ft 4 fold rule scales. The outer faces are more specialised. The top right face is the slide rule with three double and one single radius scales. The top left face has 1/4, 1/2, 3/4, 1 in. 1 1/4 and 1 1/2 in scales. The other two outer faces have a series of tables. The rule is ivory with nickel silver mounts.
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 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 101 closed frame slide rule made of plastic faced mahogany with a metal and glass cursor. The scales are: A{B,ISd,ITd,Td,Sd,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’. I have another similar 101 dated 1935 with a PC6A cursor.
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,ISd,ITd,Td,Sd,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 111 closed frame slide rule made of plastic faced mahogany with a metal and glass cursor. The scales are: L,A{B,C1,ISd,ITd,Td,Sd,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 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,ISd,ITd,Td,Sd,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.
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 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,ISd,ITd,Td,Sd,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 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 F4458/PC8 closed frame 10” slide rule made of plastic faced mahogany with a metal & glass PC8 cursor. The scales are the Rietz ones: cm\K,A{B,C1,C}D,L\in//{S,ST,T}. It has a red cloth covered card case.
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Heath & Co Hezzanith Navigation slide rule (made by A G Thornton in 1948). The usual mahogany & celluloid construction but with an odd plastic cursor (possibly not original). Scales are: cm\A{B,C}D\in//{S,L,T}. It has the usual Thornton green cloth covered card case. It has pasted on tables of Nautical Data on the reverse and in the well.

Thornton PIC Standard 20” slide rule dated 1935. It has a green, cloth covered, card case, Scales are: in\A(B,C)D\cm//(S,L,T). The cursor is a later replacement.

Thornton PIC 3756 20” slide rule dated 1952. It has a black, cloth covered, card case, Scales are: cm\A(B,C1,C)D\in//(S,L,T).

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,ISd,ITd,Td,Sd,C}D,P\in. There are tables on the back. It has a red card case.
Thornton PIC No. 101/PC8 closed frame 10” mahogany & celluloid slide rule with metal & glass cursor. Its scales are: cm\A{B,RC,ISd,ITd,Td,Sd,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,ISd,ITd,Td,Sd,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 112/PC9 closed frame 20” mahogany & celluloid slide rule with metal & glass cursor. Its scales are cm/F,A{B,RC,ISd,ITd,Td,Sd,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 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 No 132 20” closed frame slide rule of the usual wood & celluloid construction. It has a metal framed glass cursor with hinged magnifier and a green cloth covered card case and dates from the 1950s. The scales are: LL2,LL3,A{B,C1,ISd,ITd,Td,Sd,C}D,K//dynamo, volt (in well). There are inch and centimetre rules on the top and bottom edges.
Thornton Speed Time Distance Slide Rule, date code ‘43’. Marked with the broad arrow for the UK government and ‘Pattern 1448’. Note these mahogany/celluloid slide rules did not have a cursor as it was not needed. It has a red cloth covered card case that may not have been original.
Thornton PIC No 141 10” mahogany & celluloid, Electrical Engineer’s slide rule. It has a green cloth covered card case. Its scales are: in\sin,cos,A{B,C1,Z,centigrade,fahrenheit,C}D,T\angle,L. Date code for 1937.
Clementson pipe sizing slide rule marked ‘Made in England’. Mahogany with celluloid facing, made by Thornton. The scales are Temperature Drop (pump and gravity){Friction & Operating Head, BTU}Pipe size.
Clementson steam pipe sizing slide rule ‘Made in England’. Mahogany with celluloid facing, made by Thornton. The scales are Steam pressure(gauge or velocity related){pressure drop or velocity,lbs per hour}pipe diameter. It has a black card case.
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.
Stanley PIC No 3654 ten inch mahogany and celluloid slide rule with metal framed cursor dated 1951. Scales are: cm\A{B,C1,C}D\in//{S,L,T}. Dark green cloth covered card case. Note the metal end piece on the slide that I have not seen on Thornton branded PIC 3654 slide rules.
Thornton PIC No 4865 engineer’s slide rule, made of mahogany, faced with plastic. It is of closed frame construction. The scales are: cm\LL2,LL3,A{B,C1,C}D,K\in//{S,L,T}//dynamo, volt (in well). The rule has a green cloth covered card case. There are tables on the back. Date code '44'.
Thornton PIC No 4458 Reitz slide rule, mahogany faced with celluloid, 10”, date code ‘51’. It has a green cloth covered card case. Scales are: in\L,A{B,C1,C}D,K\in//{S,ST,T}.
Thornton PIC No 3650 ten inch closed frame mahogany & celluloid engineering slide rule. Scales are:cm\LL2,A{B,C1,C}D,LL3\in//{S,L,T}//dynamo/motor, Volt in well. It has a green cloth covered card case. Date code 8/54.
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.
Electrical & Mechanical Engineer’s slide rule dated 1939 in mahogany & celluloid with a PC7A cursor. It has a green cloth covered card case. The scales are: cm\LL2,A{B,C1,C}D,LL3\in//{S,L,T}. A pice of celluloid is missing from the back and the metal indicator is missing from the end of the slide. Dynamo & volt scales in well
Thornton PIC No 111 closed frame slide rule made of plastic faced mahogany with an unusual metal, wood, and glass cursor. The scales are: L,A{B,C1,ISd,ITd,Td,Sd,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. It dates from 1943 and other rules are known from this date with this cursor, possibly a wartime economy measure. This is a narrower rule than the one below as one edge is vertical.
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 10” slide rule with date code for 1936. Scales are: in\A{B,C}D\cm//{S,L,T}. It has a green cloth covered card case. Metal/glass PC6A cursor.
Thornton PIC no 100 5” mahogany/celluloid slide rule. Scales are: cm\A{B,differential trig,C}D\in. It has a green cloth covered card case. Metal/glass PC2A cursor
Thornton 5 inch Rietz slide mahogany/celluloid slide rule. Scales are: in\L,A{B,C1,C}D,K\cm//{S,ST,T}. It has a green cloth covered card case. Metal/glass PC3A cursor. Like the rule above it has a plain lacquered mahogany back, typical of the 5 inch wooden rules. No model number or date code but probably 1930s.
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.
PIC Standard 10” closed frame mahogany & celluloid slide rule that has a spring metal back. The scales are: in\A{B,C}D\cm//{S,L,T}. It has a black cloth covered card case with a press stud fastening flap. Its date is Ca.1920.
A G Thornton system Rietz 10” mahogany/celluloid slide rule, actually made by Nestler in Germany. This rule also appears in the 1916 Thornton catalogue. The scales are cm\K,A{B,C}D,L//{S,ST,T}\inch. It has  a black card case. A Nestler patent DRP173660 is quoted in the well and DRGM No 400076 + No 17284 on the cursor. Dates between 1909 and  ca.1916.
Thornton PIC Standard 10” mahogany/celliloid slide rule dated 4/31 in a green cloth covered card case. Scales are in\A{B,C}D\cm//{S,L,T}.
Thornton PIC No 3657 mahogany and celluloid closed frame 10” slide rule. It has a plastic cursor and a black card case. The back is plain varnished mahogany. It is very similar to a PIC Junior but has the well and reverse side of the slide covered with white celluloid which the Junior does not. Scales are A{B,C}D.
 ‘British Made’ so 1936 or earlier. The 2 Junior slide rules near the top of the page are ‘Made in England’ so 1937 or later.
Thornton 6039 ten inch slide rule, mahogany & celluloid with aluminium & glass cursor, made by Nestler, pre-WWI. Its scales are cm\A{B,C}D\in//{S,L,T}. It is very similar to the 6039½ rule above but the rulers are reversed and the inch one is only divided to eighths; neither does the cursor have a pointer. The label on the reverse is partly torn away revealing the slots in the stator typical of these German made rules. The cow hide case was an optional extra costing 2/6 in addition to the 10s for the rule with standard case.

Thornton PIC No 131/PC18 closed frame ten inch mahogany and celluloid slide rule, date coded 11/58. The scales are cm\LL2,LL3,A{B,C1,ISd,ITd,Td,Sd,C}D,P\in & motor/dynamo,volt in the well.  It has a red card case.

Thornton PIC 4864 5” engineer’s slide rule made of mahogany, faced with plastic. It is of closed frame construction. The scales are: cm\LL2,LL3,A{B,C1,C}D,K\in//{S,L,T}//dynamo, volt (in well). It has a green, cloth covered case. The back is plain mahogany.