The calculation is based in IS code and limit satate method. Both Dl 0 and Dl are measured in meters m. Yoctometre ym 1 x 10-24 m.
Two versions are given for this length calculation one using the length in metres and the other for the length in inches.
C_ len 2 times sqrt r 2 d 2 C len. One for feet and the other for meters. Therefore the expression gives the interval of time in hours before and after local solar noon that sunrise or sunset will occur. Length metres 150 A f.