The index reflects the tendency to supply weapons abroad. The data are collected by the Stockholm International Peace Research Institute (SIPRI) from open sources. To measure the volume of international supply SIPRI has developed a unique system using a total units - value of the trend indicators ??(TIV). TIV is based on well-known production and costs for the production of the main set of weapons. SIPRI TIV data does not reflect the sales prices for weapons. Therefore, it should not be directly compared with the gross domestic product (GDP), military expenses, or sales cost. The source advises us to use information as raw data to calculate trends in international weapons supply over time periods.