G. F. 323
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As a general rule the sizes of coins within any given range are normally more acceptable when each denomination is slightly larger than the one immediately preceding it. In paragraph 40 we have recommended the introduction of 20 cent, $2 and $5 coins. Bearing in mind that the minimum differences in diameter necessary to ensure adequate distinguishability to the eye and touch seem to range from about 2 millimetres between small coins to about 3 millimetres between larger coins (paragraph 8 of the Mint paper), it can be seen that if the size criterion referred to above is to be adhered to the introduction of new
coins within the existing range is not feasible. The difference in
diameter between the current 10 cent and 50 cent coins is such as to
preclude the introduction of a 20 cent coin of an intermediate size; and the $2 and $5 coins would have to be even larger than the unpopularly large $1 coin, probably at 33 and 36 millimetres in diameter. Coins of such size would undoubtedly be unpopular and the Mint comment that
experience suggests that a coin in excess of 33 millimetres fails
to circulate effectively because it is inconveniently large.
Another means of overcoming the difficulty of accommodating a progressive range of sizes within minimum and maximum limits would be to have two
overlapping size ranges distinguished by colour and perhaps by edge, for example a 20 cent coin in nickel brass which was larger than a 50 cent in
cupro-nickel. We do not recommend this course for apart from the additional cost of such a proposal Hong Kong people are used to a system of coins which progress in value with size, which, should we depart from this custom, may make the coin generally unacceptable. However, we shall recommend later that the 50 cent coin should be changed from cupro-nickel
to nickel brass.
43.
In discussing the difficulties of introducing new denominations within the existing range, we have not mentioned a vital factor, that of shape. Our present coins are round but it
appears to us that there is no overriding reason why use should not
be made of other shapes. The new denominations could perhaps all be
shaped coins, the distinguishing feature being not so much a difference
in diameter but a difference in shape. It would perhaps not be necessary to implement any change at all to the sizes of the present range. However,
it must be remembered that the size of the $1 coin is considered to be
too large and that coins of similar diameter but of different shape
CONFIDENTIAL
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