it uses an approximation of Up and Down Volume (because they are not kept by Tradingview/not accessible by Pinescript).

The approximation is:

The “up path” on the “up” candle can be approximated by ( High-Low ).
The “down path” on the “up” candle can be approximated by (High-Close)+(Open-Low).

(and similar for the down candle, like in the 1st post.)

Total path=up path + down path.

Up volume = Tick volume * up path/total path
Down volume = Tick volume * down path/total path

(description from original author: kprsa)

//PRC_Monster Cumulative Delta | indicator
//30.06.2022
//Nicolas @ www.prorealcode.com
//Sharing ProRealTime knowledge
//converted from pinescript

//U1
if(close>=open and (close-open+2*(high-close)+2*(open-low)))>0 then 
 U1= volume*(high-low)/(close-open+2*(high-close)+2*(open-low))
else
 U1=0.0
endif
//D1
if(close<open and (open-close+2*(high-open)+2*(close-low)))>0 then 
 D1 = volume*(high-low)/(open-close+2*(high-open)+2*(close-low))
else
 D1=0.0
endif
//Delta
if(close>=open) then 
 Delta= U1 
else
 Delta= -D1 
endif

if barindex>1 then 
 cumDelta=(cumDelta[1])+Delta

 if close>=open then 
  hi= cumDelta 
 else
  hi =cumDelta[1]
 endif
 if close<=open then 
  lo= cumDelta 
 else 
  lo=cumDelta[1]
 endif

 drawcandle(cumDelta[1], hi, lo, cumDelta)
endif

return