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CHAPTER II.

The Polar Planimeter.

Carriage, Carriage Vernier and Attachments.

The frame or Carriage C of the instrument carries the Integrating Wheel W together with the recording mechanism and the necessary adjusting screws. As already stated the Polar Arm is connected to the Carriage by the pivot F, while the Tracer Arm passes through sleeves or bearings on the Carriage which allows the Arm to slide backward and forward or to be rigidly clamped to the Carriage at any desired point by means of a binding screw L. Attached to the Carriage is a Vernier V called the Carriage Vernier, so situated as to allow the graduation of the Tracer Arm to work along its edge, and by its use the smallest division of the graduation is still further subdivided into ten smaller parts which in this case are one two-hundredths of a millimeter. By this arrangement the Zero of the Carriage Vernier can be brought very near to any desired point on the graduated Tracer Arm, the binding screw L tightened and the exact adjustment made by means of the slow motion screw M.

The exact point on the Tracer Arm to which for any given operation the Zero of the Carriage Vernier is required to be brought or set is, as has already been mentioned, both definitely located and recorded by expressing its position in terms of the unit of the scale of equal parts engraved along the edge of the Arm, and the point thus located and record for any given operation is called the Setting for that operation.

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