RC Shock Spring Gauge

I own a lot of 1/10th scale touring car shock springs, all from different manufacturers. I searched for a way to compare the springs, and maybe even measure the actual spring rate. And this is what I came up with. I designed brackets that fit on my caliper (Wiha DialMax).

And this is how to use it:

1. Put the brackets on the caliper
2. Insert a spring
3. Read the length (here: 27.5mm with the black spring)
4. Set tara (the scale to zero) with the caliper on top of it
5. Compress by 5mm (or more, if your scale can handle it). Don't push like I did on the photos. Push directly from above on the upper bracket.
6. Read the weight (here: 1254g, equals 12.54N)
7. Calculate the spring rate:

D = F / ΔL

D = 12.54N / 0.005m

D = 2508N/m

Same with the purple spring:

D = 6.77N / 0.005m = 1354N/m

-> The purple spring is just a bit more than half the stiffness of the black spring.