COMPACT function expects a Geo Time Series™ or a LIST of GTS on top of the stack. For each GTS instance it reads, it will
produce a GTS whith fewer values, by removing measurements which have the same value, location and elevation as the previous one. The first tick will be the kept, then ticks with value or position change will be kept. The last tick from the original gts will be copied, in order to keep the same LASTTICK.