In the beginning with Proto Sound a -1 meant ProtoSound. A -0 meant Horn/Whistle board and DCRU. Remember PS was a Command control of sorts, via bell/whistle and throttle setting.
Once PS-1 was replaced by PS-2 and DCS, -1 is Command and -0 is Conventional of some sort, usually Locosounds.
Anything up to 1999 and even some in 2000 where Protosound. Later in 2000 and up Proto Sound 2. Always check instructions and such. There were some miss marked in that transition period.
