Tag open cup - apparatus for determining the flash point of hydrocarbon liquids, usually solvents, having flash points between -17.8° and 168°C (0° to 325°F), under test methods prescribed in ASTM D 1310. The test sample is heated in an open cup at a slow, constant rate. A small flame is passed over the cup at specified intervals. The lowest temperature at which the vapors above the sample briefly ignite is the flash point. See Cleveland open cup.