(9) 
the entire operation. The remaining 25 per cent are largely contained within the 
range 35 to 60 feet. Only occasionally are values beyond 80 feet obtained, and 
when this happens an overhaul of electronic equipment is immediately indicated. 
TABLE III 
1949-50-51 Operations 
Range 
0-10' 
10-20' 
20-30' 
30-40' 
40-50' 
50-60' 
60-70' 
70-80' 
No. of lines 
42 
29 
28 
18 
15 
8 
4 
3 
% of lines 
28-6 
19-7 
19-0 
12-2 
10-2 
5-4 
2-7 
2-2 
Cumulative % 
28-6 
48-3 
67-3 
79-5 
89-7 
95-1 
97-8 
100-0 
Field Analysis 
A Geodetic unit of 8 to 10 men and latterly a meteorologist have been 
attached to the operation and performed the reductions immediately after the 
line-crossing. This has distinct advantages, as with limited ground installations 
small adjustments could be made and information gained at once as to whether 
reflights were necessary over certain lines. 
The data were prepared for each unit set-up of ground equipment as the work 
progressed, and no movement of equipment was authorized until an adjustment 
of some 20 lines was made to check the overall consistency of the measurements 
in forming geometrical patterns. If relatively large corrections were indicated for 
certain lines, the finger of suspicion was pointed at these lines as requiring re 
measurement for improvement of accuracy. Reflights have invariably confirmed 
the conclusion based upon the readjustment. 
Accuracy 
A pertinent question is “What accuracy is being obtained?”, and to answer 
this we must first rephrase the question to, “What accuracy is it thought is being 
obtained?”, for as yet we have no interior checks on position. The general picture 
may, however, be gathered from the results obtained in the first net of 74 lines 
extended 1,100 axial miles between geodetic bases, which summarized briefly is 
as follows: — 
(a) Lines of average length, 210 miles, may be measured to give a mean 
accidental error of 18 feet. 
(b) In a network in which the ratio of surplus lines to stations required to 
be fixed is 2, the probable errors in latitude and longitude are about 25 
feet. 
(c) The closure in position at the geodetic base is better than 1 in 59,000, 
and thus lends support that the intermediate stations are not likely to 
have a position error greater than the probable error, say 25 feet. 
(d) The replacement of the astronomic by shoran positioning has thus 
greatly improved the accuracy of control. 
Shoran values of position have indicated areas in the north in which the 
deflection of the vertical is over 1,000 feet. 
61667—2