A quantity value (value of a quantity – see NIST SP 811) is comprised of a number and a unit of measure (UoM) and specifies a quantity for a given bulk product.
Quantity values are typically determined by a measurement or calculated via a quantity conversion from a quantity value obtained by measurement.

Example:

You sell diesel during a shore-to-ship transfer: The transferred quantity value is measured to be 10 354.521 m³ (NOV – net observed volume) of product, which is calculated to be equivalent to 10 234.534 m³ (NSV – net standard volume).

You multiply the NSV quantity value with the price per unit of measure for diesel, to obtain the total financial value of the product sold.

Diesel may be priced at 500 € / m³  – Standard temperature: 15 °C

• m³ is the net standard volume (NSV) – specification of the quantity and standard reference temperature is important.

You multiply: 10 234.534 m³ × 500 € / m³ = 5 117 267 €, which is the financial value of your product.

Since volumes change with temperature and pressure, it is important to convert the quantity value ( here in m³) from an observed volume to a quantity value for a standard volume – i.e. at a defined standard reference temperature and standard reference pressure.