20,10,5, and 1 dollar weight gold coins
A dollar is a unit of weight defined in the Mint act of 1792. Notice the coin weighing 20 dollars, is twice the size of the coin weighing 10 dollars, and 20 times the size of the coin weighting 1 dollar.

20 dollar weight gold coin -1904
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A gold coin weighing 20 dollars known as a double eagle. Also note the "In God We Trust" inscription on a 1904 coin, this shows that contrary to what some say, this motto was on our coins long before it was re-added in 1954.

Gold coin weighing 5 dollars - 1884
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Gold coin weighing 1 dollar - 1857
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