To a stamp collector, very little. They are viewed as novelty items designed to acquire the money of non-collectors by making them seem more desirable. There is some value, but they won't be found in most stamp collecting books.
a tool that measures weight
It depends on the weight of the package or envelope. Letters weighing one ounce or less require a 49 cent stamp called a "forever" stamp.
Under one ounce.
A scale that will calculate the postage needed based on weight.
One ounce
The cost of a stamp to France depends with a number of factors, the package to be delivered, the geographical location, the weight of the goods, and the nature of goods. These are some of the factors that will determine the price of the stamp to France.
A Forever stamp is good for one ounce of First Class Postage inside the US.
Up to, but not exceeding, one ounce.
Depends on the weight of the parcel and the value of the stamps. Whatever the weight, yo can usually purchase ONE stamp that will cover the postage. For example, there is a $9.95 stamp that is often used for express mail.
A standard postage stamp typically weighs around 1 gram. This weight may vary slightly depending on the size and thickness of the stamp.
One first class stamp (depending on weight of course).
.55 cents in Euros. for a stamp within Germany, for a normal letter size and weight. I usually pay 1,20€ to send a letter to the U.S.