Quantity conversions are calculations which convert a given product quantity value to another quantity value, where the two quantities involved are different, e.g. converting a gross volume quantity value to a net mass quantity value.
Example: A crude oil tank is measured via tank dipping to contain 102 345.34 m³ (gross observed volume) of product. What is the net weight and net mass in long tons of the crude oil in the tank?
This is not a straightforward calculation:
To determine the net weight, we require the crude oil density (in air and in vacuum), potentially a sediment and water correction factor and a correction factor for the effect of temperature on the liquid product (CTL) and unit conversion factors.
Quantity conversions thus require four distinct kinds of petroleum measurement standards:
- Unit conversion standards
- Standards that define the CTL factors
- Standards that define the mass-to-weight conversion
- Standards that define the right sequence (and rounding) for the conversion calculation steps
For each of these four kinds of standards, a variety of measurement standards (including historical versions and national versions) is available, which, when combined, explain why quantity conversions are complex.