DCHP-1 Online
M.B. Hist. 
a unit of exchange equilent to the value of one prime beaver pelt, used in buying furs and bartering provisions, more usually referred to be trappers as a skin (def. 1).
See also: made beaver (def. 1) skin (def. 1)
- 1896 (1898) . . . experience has taught the hunter that he will get 50 MB for the robe be it large or small, so he cuts it down in order to make room on the sled for a larger number.
- 1958 The skin, as a unit of value, was presumed to weigh one pound and was called, technically, a "Made Beaver", or "M.B." Merchandise was priced in "M.B.'s" or fractions thereof.
- 1896 (1898) . . . experience has taught the hunter that he will get 50 MB for the robe be it large or small, so he cuts it down in order to make room on the sled for a larger number.