<prompt> Which of the following is not true regarding the second number of the instrument formula?Indicates the primary cutting edge angleThe angle is expressed as a percent of 360 degreesThis number is always 50 or lessIt can be omitted to give 3 number code  <response>: 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: Sturdevants art and science of operative dentistry, 4th edition page 311 