Since 1993, Thai Customs has also levied a 7% value-added tax (VAT) on imported goods. Duty exemptions are available for imports of medical machines, electrical devices and other products used for the country's economic development. Most tariffs in Thailand are ad valorem, while prices are cif. When ad valorem duties are applied, duties are calculated on the basis of weight, volume or unit. Some products have both ad valorem and quantitative rates. When both rates are applied to a product, the higher rate prevails. To collect tariffs on imported goods, Thai Customs uses the following three methods: (1) applying ad valorem tariff rates; (2) applying ad valorem tariff rates or ad valorem tariff rates, whichever is greater; and (3) collecting only ad valorem tariff rates. Thai Customs valuation is based on the true market price of the imported goods sold on the open market. The true market price of goods is defined as the total cash price at the time and place of importation and exportation at which goods of the same kind and quality are sold without loss and without any deduction. In fact, Thai Customs has established a Customs valuation procedure for Customs officers to follow.