//@version=6
indicator("Workshop 09 ABCD Ruler", overlay=false)
a = input.float(120.0, "A price")
b = input.float(100.0, "B price")
c = input.float(112.0, "C price")
d = input.float(92.0, "D price")
tolerance = input.float(0.05, "Equality tolerance",
    minval=0.0, maxval=0.5)
ab = math.abs(b - a)
bc = math.abs(c - b)
cd = math.abs(d - c)
geometry = a > c and c > b and b > d
ratio = ab > 0 ? cd / ab : na
retracement = ab > 0 ? bc / ab : na
accepted = geometry and math.abs(ratio - 1) <= tolerance
plot(ratio, "CD divided by AB", color=color.blue)
plot(retracement, "BC divided by AB", color=color.gray)
plot(accepted ? 1 : 0, "Geometry and equality pass",
    color=color.orange)
hline(1, "Equal legs", color=color.gray)