Volume Accumulation Percentage Indicator (VAPI) is a variation of the classic volume-accumulation indicators. It uses volume the same way as OBV except that it assigns volume weights based on intraday volatility . 

In a positive trend, if the stock price is close to a (local) new high, the VAPI should be at its maximum as well (and vice versa for a negative trend). If the market is looking for a direction, if the price is in the bottom side of his current trading range and if, at the same moment the VAPI osc slopes up, there is accumulation on the stock and that the prices should start to climb. The SELL signal is given when the VAPI decreases (distribution). Divergences are usually very effective too. 

(description from its original author LazyBear, code original from tradingview platform).

Translated by a request in the Italian ProRealTime’s indicators section.

//PRC_VolumeAccumPercent VAPI | indicator
//31.01.18
//Nicolas @ www.prorealcode.com
//Sharing ProRealTime knowledge
//translated from tradingview code
//original author: LazyBear

// --- settings 
length=10
// ---

x=(2*close-high-low)/(high-low)
tva=summation[length](volume*x)
tv=summation[length](volume)
va=100*tva/tv

r=50
g=255
b=50
if va<0 then 
 r=255
 g=0
 b=0
endif

return 0 coloured(100,100,100) as "ZeroLine", va coloured(r,g,b) style(histogram,1) as "VAPI Histogram", va coloured(128,128,128) style(line,2) as "VAPI Osc"