52 



SHORTER CONTBIBUTIONS TO GENERAL GEOL()c;Y, 1!)21. 



USE OF COMPUTEK. 



It is easy to remember how to manipulate 

 this computer, because both in multiplication 

 and division tlic start is made at the stationary 

 index, and the answer is found at the same 

 phice. Thus, in muhipHcation the multipli- 

 cand is set under the stationary index; the 

 movable index is set to the zero line of the 

 scale; and then, the movable index being 

 clamped to the underlying support with the 

 thumb an<l finger, the multiplier is brought 

 under the movable index; the product is then 

 found under the stationary index. In divi- 

 sion, the dividend is set imder the stationary 

 index, and the movable index is set to the 

 divider and clamped; the zero of the scale is 

 then brought to the movable index, and the 

 quotient appears under the stationary index. 



The computer also enables the operator to 

 read natural sines and tangents to at least three 

 digits, and by using complementary angular 

 values he can read the natural cosines and 

 cotangents. vSecants and cosecants, though 

 rarely used, may be obtained by taking the 

 reciprocals respectively of cosines and sines. 



As before stated, there is a twofold numer- 

 ical range from 0.01 to 1 or from 0.1 to 10. In 

 multiplying numbers hj numbers, it is im- 

 mateiial which of these scales is used; in fact, 

 a multiplicand can be selected in one and a 

 multiplier in another, and the product will be 

 correct. In multiplying numbers by trigo- 

 nometric functions, however, the true meanings 

 of these two number scales must be utilized if 

 the required answer is to be read as a trigo- 

 nometric function. These two scales in reality 

 represent any two number scales with a loga- 

 rithmic range of 1 , in which the calibrations of 

 one are ten times the value of the calibrations 

 in the other. This condition is not unique to 

 this computer, being present in all duplex 

 slide rules, but is mentioned here merely to 

 prevent possil)l(' confusion in the use of the 

 computer. 



It is recommended tiiat the computer be used 

 in the field for all computations, thus saving 

 the carrying of graphic charts or of a book of 

 logarithm tallies. The computer is in effect 

 a graphic tal)le of three-place logarithms 

 arranged for general computations. 



