Complex sentence: The mill was donated to the Museum in 1973 and carefully dismantled, at which time evidence was found of a previous use of the site as a Hammer mill. Re-erection and restoration of the machinery took seven years.
Split into simpler sentences: The mill was donated to the museum in 1973 and carefully dismantled. When the mill was dismantled, evidence was found of a previous use of the site as a Hammer mill. Re-erection and restoration of the machinery took seven years.