The y-length is measured, relative to O, along segments BnAn,
which are straight lines parallel to the x axis. When the y-length
is constant, the end points of the segments form a y-length parallel
curve.
In the diagram, the y-length of any segment BnAn, relative to O, is 2.
The asymptotes of the curve are x = 2 and y = 0.
The equation for the y-length parallel curve is:
x = y[(coshY)² - 1]½
Y = a/y
a is the y-length constant
in the diagram:
the value of y at B3 is 6
a = 2
the value of x at A3 is:
x = 6[{(e2/6 + e-2/6 ) / 2}2 - 1]½
= 6[(1.395612 + .716531) / 2)2 - 1]½
= 2.037239