Seems there is an undocumented value in the Customisation Kit readme in the savedata.txt file definition part (i.e. the very end), as there are 99 values defined yet 100 values in the actual savedata.txt file.
The undocumented value is the 100th i.e. after the heat signature and appears to be an entry for Player Ship Absolute Speed (it's always positive and seems to resolve the three velocity vector components).