The upper stone (weight about 1000 kilos) made more than 100 revolutions a minute.
Fine tuning the balance of the whole construction was important.
Nowadays piedras are recycled as picnic-tables (Sarvisé, Allué).
An oversized screw (caracol), moved by man-power, forced the lever down, leaving the poor olives no alternative but give up the precious liquid. The application of hot water made them so much the more co-operative.
The water-oil mixture was captured in a stone reservoir, called pila. Overflow from pila to pila purified the oil in few steps. The crust left between the mats served as a combustible or as fodder.
They had a vertical wheel, because that made the construction easier and the functioning more straightforward.
The last batán (Lacort) functioned until the early 1970s.