The estadal was a unit of length or distance in the old Castilian system of units. Since no actual Castilian standards are definitively known by the present day, the only way of determining the length of any Old Castilian unit would be to measure something in modern terms whose length was given by the Castilians in their units. And because this procedure does not give us any clue to which unit may have been the base unit and which were subsidiary units, this distinction really does not apply to the Old Castilian units here given, so all the units really have equal status. However, most references appear to have treated the vara (Castilian yard) as the base unit, expressing other units in terms of the vara.