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dàmma [Twi]

In Akan-speaking areas of West Africa, a unit of mass used for gold dust, equal to the weight of a seed of Abrus precatorius (damma-bó in Twi).

Christaller says the dàmma had a value of 2 pence 1 farthing. Referring to his Apprendix A, 1 ounce = 16 ackies = 3 £ 12 s. Two pence 1 farthing is 2.25 pence. Three pounds 12 shillings is (3×240 +12×12; = ) 864 pence, making the dàmma 2.25/864 ounces, or about 73.83 milligrams.

Christaller, page 62 and Appendix A.