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CHAPTER II.

The Polar Planimeter.

Settings.

In the case of Planimeters the Zero of whose Tracer Arm graduation is at the Tracer, the Setting in any case is evidently equal to and expresses the distance between the Tracer and the Zero of the Carriage Vernier. As the Length of Tracer Arm, which is always the distance between the Tracing Needle T and the Carriage Pivot F, is an important factor in all Planimeter calculations, this form of graduation has the important advantage of allowing this length to be at once obtained from the Setting by the simple operation of subtracting from the Setting the distance between the Carriage Vernier Zero and the Carriage Pivot F, which is a constant for any given instrument.

By placing the Zero of the Tracer Arm graduation at a distance from the Tracer T equal to the distance between the Zero of the Carriage Vernier and the Carriage Pivot F, the Setting is evidently in every case also the expression of the length of the Tracer Arm or the distance FT. Coradi has adopted this practice with his Compensating and other high grade instruments with most advantageous results.

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