Excerpt from A Determination of the International Ampere in Absolute Measure
In measurements based upon the third method the evaluation of the force or torque can be reduced to the direct comparison of two masses and the determination of the acceleration of gravity. The first... can be readily done with extreme precision; the second involves many difficulties, but these are largely offset by the facts that we have every reason to believe that in any region, geologically stable, the value of the acceleration of gravity remains unaltered over long epochs and that relative values of the acceleration of gravity at any two places can be readily determined with high precision. The latter fact enables the results obtained by this method at different times and places to be rendered strictly com parable with one another; the former renders the results obtained capable of correction at any future time when the absolute value of the acceleration of gravity shall have been determined to a higher accuracy than that with which it is now known.
For these reasons it appeared desirable that the work should be based on the third or gravitational method. Furthermore, it appeared on the whole desirable that the construction should be such that a force rather than a torque be measured. Accordingly a current weigher, or current balance, was constructed.
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