a circle
radius is 3
user measure to compute perimeter is 18.9078
(add transform OP in “tx” input $PERIMETER)

you know ,perimeter is 2πr or π*Φ

now，add other transform OP, in “tx” input 2*$PI*3
perimeter is 18.8496 :shock:

who is right?

both are correct

perimeter from measure SOP will give you length of the curve, but if that curve (representing circle in your case) is not precise enough it will not equal to perimeter of the perfect circle

try setting Divisions to 1024 on your NURBS circle, is it any closer to 2*PI*r value?
or simply keep Circle SOP as Primitive, which should give you perfect circle

thank！keep circle default parameter is right! I am not good at mathematics…… :cry: