ADJUSTMENT BY LEAST SQUARES 179 
shown under the respective columns in Table VIII. The approximations 
to m obtained by summation m’+ m+ m'’+m' are next given. The 
whole process for 80 points took 15 hours, an average of just over a 
quarter of an hour for each of the 56 gravity stations. 
The adjusted link-increment values are easily obtained from the 
calculated m’s by using equation (1), and the adjusted gravity value 
of each station relative to any one taken as datum can then easily be 
derived, and the isogams can be drawn. 
A check on the accuracy of reduction is obtained by computing 
the residual excess for each triangle. From equations (1) and (2) it 
is easy to see that the residual excess d’ is given by the formula 
dy = d, =F ZIM z Lark 3M, , 
which ought to be zero if the values m are accurately computed. The 
actual residual excesses which remained when the calculation was 
stopped at mv are givenin Table VIII, column ad’, and are seen to be 
below the agreed limit of error of 10 units. 
839 
