The scale is true (k=1) on the equator so that multiplying its length on a printed map by the inverse of the RF (or principal scale) gives the actual circumference of the Earth.
Aɣan eqqal tiditt (k=1) fal equator har anătfăs n tišijrit net fal karti t iwarat alkăd s ašrut wa yadăn n RF (meɣ aɣan wan assahat) ehak tăjililwăyt n amădăl