FA22- Now that the cartridge is installed, the spring is compressed to its set length. Make sure the outer fork tube is bottomed-out. Measure the reference distance again. In this case it now reads 80.2mm.
The difference between the two measurements is the Preload. In this example 88.4 - 80.2 = 8.2mm preload. (FYI - 8.2 is too much for most dirt bikes.)
If you need to increase preload washers can be added below the spring.
Decreasing preload can be a bit trickier. This would include shortening the spring perch.