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What is Which of the following is not true regarding the second number of the instrument formula? and explain in detail?
The second number of a four-number code indicates the primary cutting edge angle, measured from a line parallel to the long axis of the instrument handle in clockwise centigrades.
The angle is expressed as a percent of 360 degrees (e.g., 85 = 85% x 360 degrees = 306 degrees).
The instrument is positioned, so that this number always exceeds 50.
If the edge is locally perpendicular to the blade, then this number is normally omitted, resulting in a three-number code.

Ref: Sturdevant's art and science of operative dentistry, 4th edition page 311