How History Center in MT4 calculate volume from OHLC data?

 
When I download history data in form of csv file. All value in Volume column are zero after I import that file to the History Center in MT4 it can show volume. What is the formula they using for calculating the volume from OHLC data?
 
Your topic has been moved to the section: MQL4 and MetaTrader 4
Please consider which section is most appropriate — https://www.mql5.com/en/forum/172166/page6#comment_49114893
 

There is "real volume" and there is "tick volume". MT4 only uses "tick volume". Don't mix up the two.