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(8) 
In Table I the values of the 16 line-crossings reduced to sea-level are given, 
and it may be seen that the means for the two flights agree within 21-6 feet. With 
reference to Table III we see that an agreement within this range is obtained 50 
per cent of the time. The spread in each group of four is 40, 20, 84 and 25 feet, 
which reflects not only operator and other errors but also the elimination of 
certain instrumental errors due to the figure 8 line-crossing pattern. The agree 
ment of the means for the two days’ operation is representative of the work in 
general and indicates good control of all factors in so far as they can be controlled. 
The variation in measurement from day to day is beyond control and the grand 
mean may thus be expected to contribute more highly to general accuracy than 
agreement of readings on any one day. No measurements of the intensity were 
taken but all flights were made at that altitude where the incoming pulses were 
most intense and least distorted. It is stressed that the consistency of values 
obtained for any one line in one day’s operation of 8 line-crossings is an indication 
of relative accuracy but no clue is given of the extent of systematic error or of the 
effect of other conditions peculiar to the day’s operation. 
In Table II the corrections to the shoran measurement, which lead to the 
value 329-5860 in Table I, are tabulated to indicate the relative size and sign of 
the various corrections needed to reduce the measured values, plane to stations, to 
the sea-level length from station to station. In the reduction use is made of the 
best values obtainable for H, K and the delay, and to various degrees they are 
suspect and this contributes to inaccuracy. Antenna altitudes because of the non 
existence of levelling control are barometric but are nevertheless believed to be 
accurate to within 25 feet on the average. The height of the plane is, under 
certain atmospheric conditions and difficulty of correlation, susceptible to an error 
of at least 125 feet, which is reflected as an error in length of some 15 feet. 
Because of calibration difficulties the delay has been determined on a relative 
rather than on an absolute basis. The velocity used is that of Anderson and a 
calibration constant is derived in the adjustment to cause the shoran net to fit 
between triangulation bases, and if the work is done uniformly the net effect is a 
change in scale thus taking care of both calibration and velocity difficulties, which 
unfortunately we are not able to separate. The calibration constant and correc 
tion from the adjustment here indicated are obtained from the attachment of the 
shoran net to two geodetic points belonging to a loop not yet closed and thus 
subject to revision. Nevertheless the accidental error of —-01336 miles, or 70-5 
feet, the third highest in the operations, indicates an apparent accuracy of 1 in 
24,670. Since the line is the greatest measured and since no intensity measure 
ments have been made, it is likely that a falling-off of intensity relative to that for 
an average line (210 miles) has occurred and the relatively large minus correction 
to the observed value is supported on these grounds. The average correction 
without regard to sign applied to the 149 lines is 19-4 feet. 
Table III has been compiled to illustrate the number of lines for which the 
means obtained on separate days fall in groups of 10-feet difference. Thus for 29 
lines (19-7 per cent) the means were not greater than 20 feet nor less than 10 
feet apart. It may be inferred that 50 per cent of the line measurements on 
separate days are in agreement within 20 feet and 75 per cent within 35 feet for