Object: To make it easy to coversions between INCH size and MM size.
When you go to in USA, units of distance, speed, force and torque are different.
It is difficult for me to convert these units.
Thus, this function is added.
1 [inch] = 25.4 [mm]
1 [feet] = 12 [inch] = 304.8[mm] = 0.3048[m]
＊SFM = Surface Feet per Minute [feet/min]: This word is used for cutting speed.
＊IPM = Inch per Minute [inch/min]: This word is used for feed speed.
＊IPT = Inch per Tooth [inch/tooth]: This word is used for feed rate.