4 series

The Model 4 Geodimeter, introduced in the fall of 1958, measured 12 inches square, weighed about 35 lbs (plus the 12-volt battery and inverter), and had a range of 50 feet to 3 miles. New, it cost less than $5,000. But for those surveyors worried about cost, AGA promised that the initial outlay was “easily returned by the savings gained in just a few projects’ use.” “System Bergstrand” refers to Erik Bergstrand, the Swedish physicist who developed the science on which the Geodimeter rests. The first two digits of the serial number may indicate that this instrument was made in 1959. The base is marked “X590314” while the power unit is “X590316.”

Geodimeters, first developed in the 1950s, evolved quickly in the 1960s. In the “4 series” (shown in the photo), weight was scaled down to 20 pounds and measuring time was reduced from 45 minutes to 10 minutes, compared to earlier Geodimeter models.

For lightwave instruments, a complete set of measurements consisted of four separate observations: two measurements with the prism over true center, then measurements with offsets of 0.4 meters. Two complete sets of these measurements, separated by 24 hours, were made. Accuracy of the measurements could be affected by optics alignment, frequency drift, and calibration curve errors in the phase readings. Wet and dry bulb thermometer readings were taken at one end of the line and temperature and pressure readings were taken at both ends of the line both before and after measurements. Altimeter readings were also taken.

The 4D used a high-pressure mercury vapor lamp rather than a common tungsten light bulb as its light source. First manufactured in 1963, the “D” in its designation indicated that it could be used in daylight. The Coast and Geodetic Survey (C&GS) used this model throughout the 1960s.

In 1966, the 4D was modified to use a laser as its light source, in order to increase its range in moderate haze and to measure longer distances in bright sunlight. C&GS technician George Lesley replaced the mercury vapor lamp with a three-milliwatt helium-neon gas laser. The modified 4D was designated “4L,” and replaced the 2A and 4D models on the Transcontinental Traverse. Later, the three-milliwatt laser was replaced with a six-milliwatt laser and the model was renamed “4L 6A.”

AGA Geodimeter 4

Geodimeter 4 Sylinderen på toppen er er hus for en vifte innsatt pga. kvikksølvlampen.

AGA Model 8 Laser Geodimeter

The (laser) Geodimeter with the longest range (60 km), the Model 8, was released in 1968. It has been used widely in high order geodetic networks throughout the world.

AGA Geodimeter 8

AGA Geodimeter modell 8

AGA Geodimeter modell 8

AGA Geodimeter modell 8