My FG series Ohlins forks came with unmarked springs. A little research showed that this particular fork model (FG8901) should have 0.95 kg/mm springs. Also from what I found, Ohlins does not mark their 0.95 springs that come already assembled in forks. However they do mark their 1kg spring with 2 lines and 1.05kg with 3.
Example of 1.0 kg/mm spring (disregard spring on the left, it's origin is unknown)
Most of us not as "cool" as LDH and don't have daily access to Dan Kyle toys therefore one needs to improvise:
here is what I did to confirm that my 0.95kg/mm spring are indeed 0.95.
As you already know, any springs (even linear type springs) are progressive to a certain extend). Therefore to get somewhat accurate measurement, it has to have some initial preload. For my experiment, I decided to load it just past typical Free sag range (5-10mm.)
Here are my numbers:
Spring length at rest - 240mm
Spring length under 11.34kg - 228mm
Rate= weight / length difference or 11.34/12 = 0.945 kg/mm
Finally got some use out of these hand weights