- 2 -
denomination, but never with success.
Similarly 2 end 12 unit coins have, rarely proved successful. In many currencies of course the lowest coin is 5 or 10, or even 100, but the principles of the ideal sequence are unaffected.
5. The omission of a '2' in theory more than trebles the number of 1 unit coins needed, but if a coinage contains a large number of denominations they often do not 11 circulate effectively. It is difficult to generalise but experience scems to suggest that five or six denominations may in practice represent :n optimum.
6. What causes perticular denominations to be popular and others to be unpopular is rerely obvious, but the fact that a coin may be needed to operate an important group of vending machines (e.g. telephone call boxes) is no guarantee that it will circulate in adequate numbers. In the United Kingdom at least the reason for this is that most coin is drawn from the banks by shop-keepers who naturally prefer the denominations that are most convenient to handle and easiest for chenge-giving, and these are not necessarily the denominations most needed by the public for use in vending machines, etc.
Choice of Size, Shape and Colour
7. The smallest coins in common use anywhere in the world are about 15 millimetres in diameter and the largest are about 33 millimetres. Experience suggests that any coin outside these limits may fail to circulate effectively because it is inconveniently small or large. In particular countries the limits nay of course.
be narrover.
8. The minimum differences in diameter that are necessary to ensure adequate distinguishability to the eye and touch seem to range from about 2 millimetres
thus without between small coins to about 32 millimetres between larger coins; resort to other distinguishing features a satisfactory coinage of up to 7
denominations could be devised as follows:-
15 millimetres diameter
17
11
191
31
11
22
#1
11
25
11
28
311
#!
11
It is usual, however, and often unavoidable because of the constraints imposed by the coins already in circulation, to introduce the further distinguishing feature of
a difference in colour. White, bronze and yellow are the main colours available.
9.
In order to provide distinguishability to the touch it is frequently an advantage to combine a difference in colour with a difference in type of edge,
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