s/v is a measure of the degree of compaction of soil. The ZFG 3000 has an acceleration sensor attached to the base plate. The first integration of acceleration shows the velocity of the plate. And the second integration gives the deflection.

If the value of s/v is lower than 3.5 ms means: soil is compacted and it is possible to compact to higher compaction.
If the value s/v is higher than 3.5 ms: incompact like in-situ soil or if after compaction, it is not possible to compact to higher values.
The value of 3.5 ms is an empirical value, resulting from practical experience. In contrast to the static load plate, you get more information on the properties of the soil from dynamic load plate test.