If you are making complex molecules, how do you know your process is on target? Many petrochemical products contain long polymer chains that can change character quickly with only small deviations in the manufacturing process. Modern pharmaceuticals now include complex proteins and other molecules that are difficult to characterize by conventional methods. How can you be sure your thousand tons of plastic sheeting or that new wonder drug is going to meet spec? One tool to determine the nature of complex molecules is a precision viscometer. Viscosity is the internal resistance of a fluid to flow. Complex molecules typically interact with each other in a fluid and this can cause telling changes in viscosity. A polymer molecule in one state may have little interaction with its neighbors, and so its characteristic viscosity is low. In another state, the same polymer may interact strongly, and the resulting viscosity will be much higher. Measuring viscosity is often a reliable way to determine the state of complex molecules in a manufacturing process. The precision visometer is an important analytical tool in both research and production.