Our glass thermometers conform to the International Temperature Scale of 1990 (ITS-90). ASTM thermometers vary in diameter. Choose a glass thermometer by the length that will be immersed in the liquid or gas. We have partial- and total-immersion thermometers. Partial immersion thermometers are immersed in the fluid to the specified immersion depth. The remaining (emergent) portion of the stem is exposed to the air. Total immersion thermometers need to be immersed to the liquid temperature mark on the thermometer.