to use another reflector at a second station to measure a second line 

 with only one set-up of the transmitter. Thus, it is possible to establish 

 control nearly as fast as by ordinary triangulation methods. Because 

 of its range and accuracy, this instrument is considered to be probably 

 the best instrument for precise distance measurement. 



(2) Model NASM-3 



This model is an intermediate range instrument that can 

 measure lines as long as 20 nautical miles and, under proper atmos- 

 pheric conditions, obtain second-order accuracy; on shorter lines, it is 

 easier to obtain such accuracy. Some accuracy is lost, compared to 

 the NASM-2, but greater mobility is gained. Two sizes of reflectors 

 are supplied; for shorter lines, the smaller ones can be used to 

 observe more than one line at a time. For longer lines, one large 

 reflector, or a group of the smaller ones, is used at one station. 

 The NASM-3 weighs 57 pounds and a reflector 10 pounds. The weight, 

 being about one-quarter that of the NASM-2, makes it possible to 

 set up this instrument and measure distances more rapidly; a line 

 can be measured in about one hour. This instrument is considered 

 rather small for accurate base line work and rather heavy for ordinary 

 traverses; however, it performs well on long traverse lines and on 

 trilateration. The NASM-3 requires about one-half the power supply of 

 the NASM-2 and may be operated by 6-12-24- volt batteries. 



(3) Model NASM-4 



This instrument is portable and fast, but has a limited 

 range and only fair accuracy. It weighs 35 pounds, but requires 

 another 50 pounds of power supply and tripod. It operates from a 

 6-12-24- volt battery through an inverter or from any 1 10- volt line. 

 The NASM-4 has a normal range of three to five nautical miles and 

 commonly provides third-order accuracy. Any number of lines may 

 be measured for any given set-up depending upon the number of points 

 marked with reflectors. The two sizes of reflectors weigh only three 

 and four pounds and may be spotted as desired. It is possible to set up 

 and measure a line in 15 or 20 minutes. This instrument is used mostly 

 for short line traverse work. Evaluation by the U. S. Army Engineer 

 Research and Development Laboratory (ERDL) indicates that under 

 exceptional conditions lines as much as 11 nautical miles long may be 

 measured with results that meet the standards of first-order accuracy. 



b. Tellurometer 



This instrument is manufactured and sold by Tellurometer 



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