up and low volume(colored)

Hello Members,
Here is the small formula which I found somewhere, Maybe usefull for others.Thanx.

Formula:
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_SECTION_BEGIN("Up Low Volume");
UpVol = ValueWhen(C > O, V);

DownVol = ValueWhen(C < O, V);

Period = Param("Period",3,2,10,1);

UpVolAvg = EMA( UpVol, Period ) ;

DownVolAvg = EMA( DownVol, Period ) ;

Plot(UpVolAvg,"UpVolume", colorGreen,styleHistogram);

Plot(DownVolAvg, "DownVolume", colorRed,styleHistogram);

_SECTION_END();

can someone help to explain this formula.