Precision DuNouy Tensiometer, ring method, ASTM. Tensiometer gives precise readings of upward interfacial and surface tensions by the ring method to values reproducible within 0.05 dyne/cm. This instrument is specified for determining interfacial tension of oil against water by the ring method of ASTM Method D971 and solutions of surface-active agents in ASTM Method D1331. It is also specified for determining the surface tension of industrial water and industrial waste water in ASTM Method D1590. The ring and support stirrup are made of platinum-iridium wire with welded joints.