The rollers of the sieve and one of the mills, two of the three hydraulic mechanisms that have been restored and rebuilt in the cavity of the Molí de les Tres Eres watermill wheel. On the guided tour you can see them in operation close at hand. Without them it would be impossible to understand the operation of an hydraulic flour mill that for centuries was one of the few pieces of machinery known to our ancestors, who constantly depended on the wheat harvest.