When stylus A is moved along curve f(ϕ), link 1 slides in the guide o link 2 which turns about pole 0. At this, link 3 turns about pivot D and its pin a, connected by a turning pair to slider 4, moves along slot b of link 1. The number of revolutions of the measuring wheel is proportional to the integral u=c∫(r-r₀)dϕ where c = proportionality factor ϕ = angle of rotation of link 1.
$1303$LG,MO$