Percent Volume Oscillator (PVO)
PVO plots the difference between two moving averages of volume. The calculation is the same as MACD but it uses only volume data instead of prices.
When PVO hits a peak while price is moving up, this is considered an overbought condition (point A on chart below). When PVO peaks while prices are falling, this is an indication of an oversold condition (B).
PVO 
100 * (tAVGVp.z / tAVGVq.z  1) 
t =AverageType,p =Short, q =Long,s =Signal,z =Offset 
Trigger 
100 * (tAVG(tAVGVp.z / tAVGVq.z, s)  1) 

Histogram 
100 * (tAVGVp.z / tAVGVq.z  XAVG(tAVGVp.z / tAVGVq.z, s)) 
Where t
is the average type. Leave blank for Simple, X for Exponential, F for Front Weighted, H for Hull.
Where p
is the short period which must be an integer.
Where q
is the long period which must be an integer.
Where s
is the signal period which must be an integer.
Where z
is the offset. An offset of 1 would return the value for the previous bar instead of the current bar.
Examples
An exponential price volume oscillator 12,26 can be written as follows.
100 * (XAVGV12 / XAVGV26  1)
The 9 period exponential trigger of the exponential PVO 12,26 can be written as follows.
100 * (XAVG(XAVGV12 / XAVGV26, 9)  1)
The exponential PVO Histogram 12,26,9 is the raw PVO minus its trigger and can be written as follows.
100 * (XAVGV12 / XAVGV26  XAVG(XAVGV12 / XAVGV26, 9))
Read more about volume oscillators at Investopedia