First compiled by Paul Wise 2014,

Updated August 2016



In May 1954, National Mapping received a Geodimeter (a name derived from GEOdetic DIstance METER) Model NASM-1, manufactured by AGA (Aktiebolaget Gasaccumulator) of Sweden. The fact that Natmap and Australia operated this equipment seems to have been missed by authors of papers of that era; it appears that only Clark (1963) makes any mention of the fact. Nevertheless, National Mapping’s use was documented by Rimington (1956), Waller (1956) and Ford (1979). Today the term Electronic Distance Measuring (EDM) equipment covers any device that uses an electronic means to measure distance and the NASM-1 Geodimeter was not only an EDM instrument but in fact the first line-of-sight EDM instrument.


Geodimeter NASM-1

Problems with maintaining and monitoring a stable frequency electrical signal emerged with the adoption of the telephone and the evolution of broadcast radio. While investigating these problems in 1927, Canadian Warren Alvin Marrison developed a highly accurate clock. Marrison’s clock was based on the regular vibrations of a quartz crystal in an electrical circuit. Quartz clock operation is based on the piezoelectric (electricity resulting from pressure) property of quartz crystals. The interaction between mechanical stress and electric field of a quartz crystal in a suitable electronic circuit causes the crystal to vibrate and generate a constant frequency electric signal. This signal is then divided up electronically until the number of pulses reaches 60 per minute and the output fed to the (analogue and later digital) clock display.

While at the Nobel Institute of Physics in Stockholm, Sweden in the latter 1940s, Dr Erik Osten Bergstrand developed an instrument to measure the speed of light. At its heart was the ability to use a crystal to control the emitted light so that its behaviour was consistent. His first trials required an instrument at both ends of a line of known distance, but this was soon replaced by a single instrument and a mirror reflector. In 1947, Bergstrand took his instrument to a 7,734m baseline and obtained a measurement of 299,793.1 ±0.2 km per second for the speed of light. (Bergstrand’s value for the constant was very close to today’s value of 299,792,458 ±1.2 metres per second). In 1947 when he had a value for that constant, Bergstrand could adapt his device to obtain the distance between any two intervisible points (Bergstrand, 1949). Bergstrand took his idea to AGA who built a prototype in 1951 and then produced the first commercial model of the Geodimeter, the NASM-1 in 1953. Thus EDM was born!


1954 National Mapping Council Members inspecting the Geodimeter NASM-1.
(L-R) Unknown, Unknown, WV Fyfe (Surveyor General Western Australia), ED Blackwood (Surveyor General & Secretary for Lands Tasmania), GW Vincent (Surveyor General & Director of Mapping New South Wales), JNC Rogers (Commonwealth Surveyor General), Col. L FitzGerald (Director of Survey, Department of the Army, representing the Commonwealth Survey Committee), ED Mellor (Acting Surveyor General Queensland), FW Arter (Surveyor General Victoria), GRL Rimington (Chief Topographic Surveyor, National Mapping Office), HL Fisk (Surveyor General South Australia), Dr KW Rohnstock (Assistant Director of Mapping New South Wales), BP Lambert (Director of National Mapping).

Photograph below taken from reverse direction.



The light emitted by the NASM-1 was projected in pulses at 1/10,000,000 of a second (100 Nanoseconds) duration in groups of 100,000 or of 1/100 of a second duration. A delay of 500 Nanoseconds occurred between each group. Comparing the phase shift of the incoming signal to the outgoing signal provided the distance information. Ambient sunlight affected the reflected signal which degraded the accuracy of the measurement, making it necessary to take observations only at night. In fact Waller (1956) stated that during one night, measuring was delayed by moonlight swamping the reflected Geodimeter signal.


Geodimeter NASM-1 in Australia

The then Deputy Director of National Mapping, Bruce Lambert, saw the Geodimeter concept demonstrated at the International Union of Geodesy and Geophysics congress in Stockholm in 1948 (Lines, 1992). While Lambert had some initial concerns about the introduction of such electronically complex equipment into his organisation, these doubts were dispelled after discussion with Australian scientific experts.



Photograph of assembled Measuring Unit and Light Conductor components of NASM-1 Geodimeter with enlarged identifying plates inset.


The production of the AGA NASM-1 was limited to ten units. Of these, American mapping organisations bought five of the ten instruments (Smithsonian, 2014) and most likely the South African’s one instrument (McLean, 2015) as well as the British. As the serial number of the Natmap unit was 7, AGA/Sweden probably kept unit 1 with units 2 to 6 going to the Americans and two of the remaining three units supplied to South Africa and Britian.


Soon after Natmap’s Geodimeter arrived in Australia, Natmap found that its successful deployment and use required several prerequisites. The measuring and optical units together weighed some 100kg, so the sites at which the measuring unit could be used required vehicle access. Transportation over Australian outback roads also needed to be considered. An International two wheel drive, 10 cwt panel van was obtained to meet these requirements. A Landrover with trailer acted as a support vehicle and carried the reflecting mirrors. For relatively short distances over rough or steep terrain for which the International was not designed, the Landrover could be pressed into service to carry the Geodimeter to the required site. A zoomable picture of Natmap’s former NASM-1 operating panel can be viewed via this link.




Measuring with the Geodimeter NASM-1.

Typical setup with Keith Waller at the control panel (left) and Bob James assisting (right).


The table on which the Geodimeter unit sat was specially designed. Triangular in shape, the steel table had legs that could be removed for transport. When assembling the table the length of each table leg could be individually adjusted to provide a horizontal table-top. The adjustable table legs in conjunction with the Geodimeter’s own level adjusting screws meant that a measuring site needed no special preparation. A tent with a tubular steel frame was designed to shelter the equipment and a generator (unspecified) provided power. After being driven to South Australia as part of the test program, it was found that dust-proofing the Geodimeter’s container would also be advantageous.


From August 1954 until March 1956 the Geodimeter was employed to measure various base-lines in Victoria, New South Wales, South Australia and Queensland. Some of these base-lines had been measured to a high precision with invar bands (which are made of almost expansionless metal) and some of the base-lines had been computed through the trigonometrical network. In 1955, a Spherical Reflex Mirror for use at the distant station was received. It was designed to eliminate the trouble experienced with light beam shifts caused by vertical refraction and to evaluate its effectiveness at least one line was remeasured with this new mirror and the original Plane mirror.



Spherical Reflex Mirror at the distant station being aligned by Norm Hawker.




Photographs of the stored Spherical Reflex and Plane mirrors, June 2015 (courtesy Kaye Nardella).


For the most part the Geodimeter had no trouble in measuring lines up to 15 kilometres and if everything went right up to 25 kilometres but this was only achieved once. Accuracy was of the order of 1 part in 200,000 or an error in the distance measured equivalent to 5mm for every kilometre. Such accuracy was comparable to that obtained by any high precision base-line invar chaining. ests by the American Army Map Service in co-operation with the British Ordnance Survey produced results that were accurate to 1 part in 300,000. Both these organisations also agreed that the accuracy of a measurement with the Geodimeter was comparable to the accuracy from chaining the line using the best invar tapes. The Australian tests resulted in the conclusion that the NASM-1 Geodimeter could measure distances with a limiting error of ±0.08 feet (approximately ±1 inch or ±24 millimeters).


In Australia in 1955, it was thus foreseen that with the Geodimeter available to measure the side of a triangle every 400km or so in the main triangulation network, there would no longer be a need for tedious base-line measurements, or the observing of the associated and time consuming base-net triangulation schemes. This view was probably due to the 1954 success of the Geodimeter in measuring selected lines within the newly completed triangulation between Broken Hill, Orroroo and Carrieton. National Mapping fieldbook 423 (black) recorded Bergstand Geodimeter Number 107 - Line Observations : Carrieton Base : Maurice Hill - Black Rock [Orroroo] : Feldspar - 20 mile [Broken Hill](sic).




Geodimeter Model NASM-2


In June 1956, a new Geodimeter was tested by National Mapping before being loaned to the Western Australian Lands Department. For the next 2 years this Geodimeter was in almost constant use before being phased out in 1958. This instrument was a Geodimeter NASM-2. The NASM-2 was introduced in 1955, and by 1957 some 50 units were in use world-wide. The Model 2 Geodimeter resembled the Model 1, but used three modulating frequencies rather than two and its new light source also increased its range to about 50 kilometres.


National Mapping used the Geodimeter for the last time in March 1958. During that month a series of measurements for the Tasmanian Department of Lands and Survey were undertaken. On conclusion of that program various models of the Tellurometer were then used for electronic distance measurement by Nat Map until the arrival of the Model 8 Geodimeter (Laser) at the end of 1968 (Ford, 1979).



Legacy of the Geodimeter

As organisations evaluated the Geodimeter NASM-1, they used Bergstrand’s value for the speed of light in the reduction of their observations to find the distance measured. These data combined with more laboratory observations suggested a better value for the velocity of light in vacuo.


Saunders (1965) stated: The Geodimeter has been used since 1950 on several occasions over different baselines to measure the velocity of light. Bergstrand himself (1951), obtained a value of 299,793.1 ±0.2 km/sec by combining his earlier measurement with a new determination over a 5.4km baseline on the island of Oland. Mackenzie (1954) in Great Britain obtained a result of 299,792.3 ±0.5 km/sec, Scholdstrom (1955) in Sweden obtained 299,792.4 ±0.4 km/sec, and Waller (1956) in Australia, 299,792.5 km/sec.


In 1957, these results led the 12th General Assembly of the International Scientific Radio Union to recommend the adoption of 299,792.5 ±0.4 km/sec as the velocity of light in vacuo. This value was later accepted by the International Union of Geodesy and Geophysics and subsequently adopted by the National Mapping Council of Australia in March 1958 (Lines, 1992).


While the Geodimeter gave Australian surveying and mapping organisations a vision of the possibilities for future EDM use, the Geodimeter also had its limitations. It was heavy and only usable at night over a limited distance. Further, it was complex to use as was the calculation of the distance measured. These limitations were really exposed when the South African developed and manufactured Tellurometer became available. The micro-wave based Tellurometer was relatively lighter and hence more portable than the Geodimeter. It could be used day or night over longer lines and measurement and reduction was more easily accomplished. Even though a unit was required at both ends of the line to be measured, the combination allowed for voice communication between the units. At a time when light-weight portable transceivers were not common this facility was a valuable asset during survey operations. A limitation for the first Tellurometer model the MRA-1, was that the units came as a pair, a Master and Remote; measurements could only be made with the Master unit. When using the MRA-1, National Mapping adopted the practice of measuring each line twice, by swapping the Master and Remote units between the ends of the line being measured.




MRA-1 Tellurometer (left) and operating panel (right).


In July 1957 the first Tellurometer was tested in Australia (model MRA-1, S/Nos MA11 [Master] & RA11 [Remote]). A comprehensive measuring program was undertaken in the Northern Territory. All lines were measured in the triangulation figures in the Wauchope area followed by sixteen lines of the traverse northward to Powell Creek. Two separate measurements were taken along each line, as described above. By 1959 Natmap had four pairs of model 1 Tellurometers, serial numbers 11, 40, 74 and 318 (Rimington, 1960). The Tellurometer proved its worth, and thus a succession of Tellurometer models, namely: the MRA-2, -3, and -4 were all used by National Mapping until around the mid-1970s.


National Mapping's extensive evaluation of both the Geodimeter and Tellurometer, supported by the consistent results obtained by other user agencies, saw the National Mapping Council in 1959, accept its Technical Subcommittee's recommendation for the future use of the Geodimeter and Tellurometer. In essence, it was the Subcommittee's view that (a) Geodimeters were best for measuring lines of length of 1 to 20 miles with an average accuracy of 2 parts in 1,000,000 (0.06 metres in 30 kilometres) and (b) Tellurometers were best for measuring lines of length of 10 to 50 miles with an average accuracy of 5 to 10 parts in 1,000,000 (0.8 metres in 80 kilometres) (Rimington, 1960).





Operating panels of Tellurometer models (left to right) MRA-2, 3 & 4.


The AGA (laser) Geodimeter Model 8 with a range of 60 kilometres was released in 1968 and two were purchased by National Mapping that same year. Instrument S/N80005 was delivered in November 1968 and Instrument S/N80002 in March 1969. Neither passed acceptance testing and were replaced by the manufacturer. Instrument S/N80028 was received in May 1969 and Instrument S/N80053 in September 1969. After exhaustive testing both Geodimeters were accepted and performed well (Murphy, 2014). Further Model 8 operating details can be found via this link.




A Model 8 Geodimeter (left) and its operating panel (right).

The operating panel pictured is that of S/N 80005 mentioned above.


The Model 8 Geodimeters were acquired for the proposed national high precision traverse program to inter-connect the capital cities and so improve the existing Tellurometer traverse and triangulation. This program also proposed the re-measurement of existing triangulation baselines and was then estimated to take 8 years.


Soon after commencement, the re-measuring program was cancelled and the Model 8s were then used in the Papua New Guinea plate tectonic surveys of 1973 and 1976 and the Australian Capital Territory Precision Control Network Survey of 1972. The Model 8s were also loaned to State Lands Departments to help strengthen their networks. Nevertheless, remeasurement of the traverses connecting the Johnston Origin to the capital cities of Perth, Adelaide, Melbourne, Sydney and Brisbane as well as the PAGEOS baselines, was achieved.



A 1968 photograph of Bob Bobroff demonstrating the operation of Model 8 Geodimeter (S/N 80005) to Bruce Lambert the Director of National Mapping.


Interestingly, on the Mackay - Townsville section of the geodetic survey, Natmap used its brand new MRA-4 model Tellurometers. The MRA-4s signal, however, was unable to penetrate the high humidity atmosphere, filled with smoke from sugar cane fires to get a distance measurement. The required measurements were finally achieved, albeit at night, with the Model 8 Geodimeter.


In order to ensure that maximum accuracy was being achieved with their MRA-4 model Tellurometers and model 8 Geodimeters, in 1971 Natmap tested 4 units (2 of each). A 22.8 kilometre line was selected near Canberra and over a 24 hour period a rigorous test regime was followed. The test is fully documented in Natmap’s Technical Report 14 available here.




An example of one of the many models of total stations available


Total Station

Where once the surveyor needed a theodolite to measure angles and an EDM to measure distance, sixty years on both requirements are today combined in the total station. Nevertheless, as a result of the work done in evaluating the NASM-1 Geodimeter, the 1958 value for the speed of light (plus or minus a few decimal places) is coded into the heart of the electronics of these devices enabling distance to immediately be displayed to the surveyor.




The assistance of Brian Murphy in providing details of the Model 8 Geodimeter is greatly appreciated. The recent photographs of the former Natmap NASM and its reflectors, now held in storage in Queensland, provided by Laurie McLean, and Kaye Nardella (Senior Curator, Museum of Lands, Mapping and Surveying) with the support of Bill Kitson are also gratefully acknowledged.






Bergstrand, Erik Osten (1949), Measurement of Distances by High Frequency Light Signalling, Bulletin Geodesique, Vol.11, No.1, March 1949, pp.81-92.


Clark, David (1963), Plane and Geodetic Surveying for Engineers, Vol.2, 5th Edition, London, Constable & Co. Ltd. pp 281-291.


Ford, Reginald Arthur (1979), The Division of National Mapping’s part in the Geodetic Survey of Australia, The Australian Surveyor, Vol.29, No.6, pp.375-427; Vol.29, No.7, pp.465-536; Vol.29, No.8, pp.581-638.


Lines, John Dunstan (1992), Australia on Paper – The Story of Australian Mapping, Fortune Publications, Box Hill.


McLean, Lawrence William (2015), The Division of National Mapping’s Aerodist Program 1963-1974


Murphy, Brian (2014), Personal communication March 2014.


Rimington, George Robert Lindsay (1956), Introduction to the Geodimeter, Cartography, Vol.1, No.3, March 1956, pp.120-124.


Rimington, George Robert Lindsay (1960), Report on Electronic Distance Measurements in Australia, Journal of Geophysical Research, Vol.65, No.2, pp.430-435


Saunders, JH (1965), Velocity of Light, Pergamon Press, Oxford, pp.32.


Smithsonian (2014), EDM (Geodimeter Model 2A), accessed at :


Waller, Charles Keith (1956), Field Use of the Geodimeter, Cartography, Vol.1, No.3, March 1956, pp.125-130.


Wennstrom, HF (2014), Erik Bergstrand and The Geodimeter accessed at :