Welcome to northern Ozarks testing.
I had a lot of fun in the shop tonight.
Decided to make a spring rate tester.
Most spring rate testers push down on the spring and a load cell calculates and displays the rate.
My tester pulls up on the spring to compress it and a load cell displays the rate.
Either way will work in my opinion.
I have four stock rear oddy springs and I tested them all.
If you look at my test rig it is just a chain welded onto a plate and pulled through the center of the spring with a come-a-long. A load cell is hooked between the chain and the come-a-long.
On the first try it pulled the spring crooked so I had to put it into a tube. I measured from the end of the load cell hook to the top plate on the spring and then used the come-a-long to pull it up 1".
I got the same reading on all four springs to within a decimal point on the first try of every spring. So that tells me this is accurate.
The scale shows 208 lbs/in.
Most of us (including myself) thought the stock springs were 223 lbs/in. This test tells me the stock rear springs are actually 210 lbs/in.

Brilliant work CO

Very cool! Thanks for posting!

Update to this thread.
I checked my brothers aftermarket springs tonight.
These springs were on the machine when I bought it.
The rate came in at 135 lbs/in.
I tested it a few times to make sure.
Pics below.