From Wikiwand: Maxwell (unit):

This practical unit was previously called a line,[4] reflecting Faraday's conception of the magnetic field as curved lines of magnetic force,[5] which he designated as line of magnetic induction.[4] Kiloline ($10^3$ line) and megaline ($10^6$ line) were sometimes used because 1 line was very small relative to the phenomena that it was used to measure.

So how is a “line” measured? Does anyone have specifics on this measurement?