Convert from cover to dunum, dunham

Unit Definition (cover)
The Cover is a traditional Welsh unit of area, standardized in the British system to be exactly 2/3 acre (about 0.2698 hectare). The word is an Anglicized version of the Welsh name cyfair for the unit.

Unit Definition (dunum, dunham)
The Dunum is a traditional unit of land area in the Middle East and the Balkans. The unit is of Turkish origin, but it seems to be obsolete in modern Turkey. As it is commonly used today in Israel and Palestine and in Croatia and other areas of the former Yugoslavia, the dunum is a metric unit equal to 1000 square meters or 0.1 hectare (about 0.2471 acre). The traditional size seems to have been around 900 square meters. In Mesopotamia and Arabia, the dunum was a larger unit, traditionally in the range of 2500 to 4000 square meters. In modern Iraq, the dunum is now standardized at 2500 square meters (about 0.6179 acre).