A coomb is a measure of volume. Its exact original details are not known. In 13th century England it was defined as 4 bushels (~140 L). It was in use in Norfolk until the 1790s or later, as a dry measure: "Ben sold my Wheat to the Marlingford Miller this Morning for 19 shillings per Coomb" - Parson Woodforde's Diary, May 20, 1786. The 4-bushel bag was the standard international shipping unit for grain, and the coomb was in common use in farming in Suffolk until well after the end of World War II, in fact for as long as grain was handled in sacks, a practice which ended with the introduction of combine harvesters which had bulk grain tanks.
Yields were referred to in coombs per acre. A coomb was 16 stone (100 kg) for barley and 18 stone (110 kg) for wheat. The US grain markets quote prices as cents per bushel, and a US bushel of grain is about 61 lb (28 kg), which would approximately correspond to the 4-bushel coomb (4 × 61 lb = 244 lb ≈ 111 kg).
Although seldom referred to in Suffolk today except in conversation, older farmers in North Germany will frequently refer to crop yields in Doppelzentner pro Morgen. The area of a Morgen varies a bit in different regions, but is believed to be derived from the area a man would plough in a morning (Morgen), and is about one third of a hectare (0.82 acres), which is similar to an acre. A Doppelzentner is 100 kg (220 lb), and thus similar to a coomb. Similarly, the German word for an area of arable land is an Acker. It is easy to infer that the imperial acre is derived from the same Germanic word base. Thus the English and the German yield units are thus closely related, coombs per acre being similar to Doppelzentner pro Morgen.