124 E. E. ROSAIRE AND JOSEPH L. ADLER 
out regard to sign to obtain the misclosure frequency curves repro- 
duced in Figure 2. The number of occurrences of each misclosure has 
been laid off vertically. The amount of the misclosure to the nearest 
10 feet is indicated along the horizontal axis. 
A radical break in the original irregular curve will be noted at 
about 250 feet. This break may indicate that the errors in excess of 
250 feet, which are obviously more frequent than errors near 250, are 
due to some special conditions or to gross personal errors occurring 
on a few traverses. The nature of such special conditions is discussed 
later, but it may be said here that they are probably geological. 
FIGURE e. 
Frequency 

t) ' z 3 4 5 6 1 8 9 0 
Misclosure in Hundreds of Feet 
Fic. 2.—Frequency curve showing misclosure on 151 traverses. Horizontal co-ordinate 
of point P equals probable error. 
To bring out this break, separate curves, numbered 1 and 3, have 
been fitted to the two portions of the original curve. Curve 1 may 
indicate the frequency of the usual errors encountered in dip shooting, 
while curve 3 may indicate in part the frequency of large errors due to 
special conditions. If that is the case, it would be advisable for the 
geophysicist to investigate any misclosure in excess of 250 feet which 
he may encounter in the course of his work, to discover if some pecul- 
iar geological condition such as faulting or terracing is not present. It 
may be, however, that the break noted in the curve is simply an ac- 
cident due to insufficiency of data. 
Curve 2 is an exponential curve representing the mean of curves 1 
and 3. It approximates very closely the curve best fitting the original 
data. It is, moreover, capable of formulation as follows. 
Equation (1) x=3.1—1.23 log y where x equals the misclosure in 
hundreds of feet and y equals the frequency of occurrence. 
From this equation the probable error in the traverses analyzed 
may be computed. The probable error has been defined as “‘that error 
646 
