CHARTS FOR TORSION BALANCE READINGS 31 
where 7, is the reading of the instrument in its kth position, and 
No = 3(m + ne + HN). 
The unprimed letters refer to the quantities bearing on the one beam, and 
the primed to those on the other beam. 
The originals of the charts are 20’’ X20”’ with the horizontal and vertical 
scales running from —10 to +10 units at intervals of 0.1, a range well within 
that usually necessary. 
It has been found that nomographs are not quite as convenient as these 
charts for field use. 
175 
