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Wartime Information Board was created in 1942.
The Chicago Board of Trade has the prices. Other sites, including tradingeconomics, show prices from the past thirty years or so.
When prices are low, trade decreases.
Wallace Cause Willson has written:
'Weekly prices of butter on the Elgin Board of Trade from 1880 to 1912 ..'
Brampton Board of Trade was created in 1903.