A test to measure static filtration behavior of water mud or oil mud at elevated temperature, up to about 380掳F (193掳C) maximum (450掳F (227掳C) maximum if a special cell is used), usually according to the specifications of API. Although the test can simulate downhole temperature conditions, it does not simulate downhole pressure. Total pressure in a cell should not exceed 700 psi (4900 kPa), and the differential pressure across the filter medium is specified as 500 psi (3500 kPa). Because these cells are half the size of the ambient filtration area, HPHT filtrate volumes after 30 minutes are doubled.