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The denomination (or value) of a stamp is the amount
of money (in some currency) for which it pays postage or other
fee. The denomination is typically expressed as a number followed by
an abbreviation for a unit of the currency, for instance "40c".
The number in the denomination may be a decimal value, a fraction, or a combination of whole number and fraction, as in "1 1/2d". Combinations are also possible, as "2sh6p".
The currency unit must be one of those in the currency definition. This goes for the dollar sign as well, which is different from standard usage.
Semi-postal stamps express the additional charge with a "+", as in "2d+25p" for a 2-dinar value with a 25-para charity surcharge. If the surcharge is not written on the stamp, it may be parenthesized.
(mention dual denomination)