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Interception Plotter


1) The instrument is contained in a grey plywood case with a white fabric strap afixed to the sides with metal fasteners. “INTERCEPTION PLOTTER V2074 SERIAL NO 539” is stenciled in white on the front of the box. Glued inside the lid of the box are packaging, assembly, and fitting instructions along with several wooden supports with green fabric (felt?) padding. Two of these supports are missing. The bottom of the box has wooden dividers and supports too, many of which are lined with the same fabric. On the left side of the bottom of the box is a metal cylinder about the size of a roll of masking tape attached on an angle to the box. There is a broken piece of wood and felt that was once attached to the right interior of the box.

2) A wood rectangular bar (224mm x 37mm x 19mm) with rounded corners on one face. The wooden bar has a rectangular shape cut away from it that has been lined with green fabric (felt?). There is a smaller rectangle cut away part way up the felt. There are two holes at each end, likely to allow for screws to pass through the bar. It is suspected that the wood bar is a removable part of the box.

3) A large heavy metal structure. It has a rectangular metal frame with a plate containing gears and swiveling parts on the top side. Extending from the interior of the frame is a metal arm with a metal disc at the end.

4 and 5) two wide, clear plastic rulers. There are 2 plastic rotating circles at either end. In the center, there is a black metal circle. Between the center metal circle and one of the clear circles is flat, rectangular box with rounded edges. It is black and has a metal button affixed to its side.

6) One clear plastic measuring tool shaped like a large, flat thermometer

7) One metal disk with a slit cut out of it. It has white paint and says “wind from”

8 ) One loose paper tags that says “WARNING Do not attempt to remove this instrument from transit case until the four securing screws have been taken out.” It has a string attached (note: there is an identical tag glued into the bottom of the interior of the wooden box).

10 and 11) Two metal counting devices made by Veeder attached to L-shaped brackets

12) One circle attached to an L-shaped rod which resembles a small desk light.

13) Various small metal parts including nuts and screws.

Accession Number: 2016.zoo.5

Alternative Name:

Primary Materials: Wood, metal, plastic, paper, cloth


1) The exterior, top of the box is stenciled with “DELICATE INSTRUMENT HANDLE WITH CARE”. The front of the box is stenciled with “INTERCEPTION PLOTTER V2074 SERIAL NO 539”. The interior of the box lid contains three labels one titled “PACKAGING INSTRUCTIONS FOR INTERCEPTION PLOTTER”, one titled, “INSTRUCTIONS FOR RIGHT AND LEFT HAND ASSEMBLY OF INTERCEPTION PLOTTER”, and one titled “INTERCEPTION PLOTTER FITTING AND ADJUSTMENT OF PERSPEX SCALE”.

2) The wooden bar has the letter “A” stenciled on it.

3) Large heavy metal structure has notched numbers and “KNOTS X10”, “N.M.P.M.”, “PORT DRIFT” “ST’BD DRIFT”; “HI…ED SCALE RED” “LO…ED SCALE YELLOW”, “…NLY ONE COLOUR MAY BE USED IN …NY CALCULATION”. There is a metal plate lower down on the structure that reads “PLOTTER INTERCEPTION. REF No. V.2074 SERIAL No. 539. KELVIN AND HUGHES LTD. MADE IN GREAT BRITAIN”. There are also gears on top one of which says “BOS” “TON” “G-” “149” and the other which says “BOS” “TON” “U.S.A.” “G-” “149”.

4 and 5) the clear plastic rulers “TIME MINS”, “DIST. MILES”, “TIME MINS” “DIST. MILES” and numbers

6) flat thermoter-shaped tool “TRUE AIR SPEED”, “KNOTS X10”, and numbers

7) metal disk “WIND FROM”, “KNOTS”, and numbers

8 and 9) two paper tags with “WARNING Do not attempt to remove this instrument from transit case until the four securing screws have been taken out.”
10 and 11) counting number devices “Veeder” “VEEDER-ROOT LTD DUNDEE, SCOTLAND”
12) “3V.19A” on top of the circle
13) n/a

Dimensions (cm): 709x254x178


Interception plotters were used to track the movement of planes. The plotters were used to calculate direction and speed of aircrafts based on radar displays. It was used in Ground Control Interception sites that were designed to provide early warning of raids. The large metal structure (the fixed calculating head) would be attached to an arm that terminates in a moveable ruler.


The exterior of the interception plotter is dust, scratched, stained and the paint has been worn away. The strap on the exterior is slightly frayed and has a small whole near the right side. There is a wooden splitter that has been broken off the right interior of the box. The interior of the box is dirty.

The arm of the large metal structure has a silver piece that is bent. The large metal structure is dirty. The same piece has white residue, suggesting corrosion.

The metal disk has a white coating that has been chipped.

There are two wooden supports missing from the top of the box. The instrument is in pieces and there are probably missing screws.

Associated Instruments:

Manufacturer: various, including parts from

Date of Manufacture: 1939-1960s?


Owned by the University of Toronto’s Department of Zoology. Donated to UTSIC in November 2015. It had most recently been stored in the department’s ‘workshop’.

Additional Information and References:

Interception plotters may be called “Craig Computer” or simply “plotters”.

On Monday March 21st, Orvis Starkweather met with Nalini Singh for research assistance. Nalini was able to locate a Royal Institute of Navigation newsletter pertaining to interception plotters but little else. She advised making an appointment to talk to someone at the University of Toronto Archives and Records Management Services as the next step to tracing a U of T connection to the object.

Hope-Lang, Keith. “Interception Plotter/Craig Computer.” History of Air Navigation Group Newsletter No. 22 (June 2013): 4-6. Royal Institute of Navigation. June 2013. Web. 30 Mar. 2016. < Newsletter 1306.pdf>.

Historical Notes: