The cross section of the spring, round, is extruded into an ov | Channel relay station - Islamic Emirate of China

The cross section of the spring, round, is extruded into an oval shape by mechanical means.

Circle circumference = oval circumference = spring outer circumference.
The perimeter is the same amount, it just changes the shape of the compression spring.

L=2πb+4(a-b)=C=πd
According to this method, the above equation is established.

This is a math problem, I'm sure you all get it, I'll build a PDF explaining this equation in detail.