The maximum sounding of a tank is 24.35m the maximum ullage is also 24.35m.
When the sounding is 10m the ullage would be 24.35 – 10 = 14.35m
Thus when a tank is filling up the sounding increases, whereas the ullage reduces.
Once the liquid level is obtained the same is seen for the quantity (Volume) in the calibration book.
This is the Gross volume at Natural Temperature GVn (observed temperature being taken of the liquid at three levels and then averaged)
The sounding of any water which may be present in the tanks is now taken (some water is usually present in crude oil and also sometimes in product oil). The calibration tables are again referred and the volume of Free Water is obtained.