The series, coin by coin

A rank of "20th of 32" does not tell you at a glance whether a coin is unusual, so every coin carries a dot. Scarce is deliberately the small band: 17 per cent of the coins that get one.

What it measures. This coin's figure against the typical figure for its denomination, which is the median. Scarce is under a third of typical, common is double it or more, and the ratio is printed beside the label so you never have to take the label's word for it. The 1925 penny is 0.28x a typical penny; the 1953 penny is 8.08x.

Why a median and not a share of the total. Because there is no honest total. A mintage figure is meaningless without knowing what it counted, and this catalogue holds four kinds: coins issued, coins delivered, coins struck during a report year, and a mint's own published summary. Twelve of the sixteen denominations mix them; the penny is 47 per cent issued, 34 struck-dated, 10 delivered, 9 report-year. Adding those into one number would be the exact conflation this catalogue exists to refuse. Comparing one figure against a typical figure needs no addition at all. It is still a comparison across bases and so it is approximate, which is why it is a dot and a ratio rather than a claim.

A dot cannot tell you which variety you have, because where a date covers several documented varieties the mintage covers all of them together. That is why the variety flag sits beside it as a separate signal, and why the 1920 penny is ordinary and still the last coin you should bag unlooked-at.

Nor can it see which mint struck yours. Australia had branch mints at Melbourne, Sydney and Perth, and in a single year one could make seventy times what another did: in 1946 Melbourne struck 187,200 halfpennies against Perth's 13,560,000. Every issue that has one now carries that breakdown, because a single figure hides it completely. Most pre-decimal coins carry no mintmark, so you usually cannot tell which you are holding by looking, and where a mark exists the attribution is often contested.

Silver and gold are a separate question and keep their own chip. A coin can be common and still be worth more than face value because of what it is made of. The metal calculator works out what is in one.

The thresholds are a choice; the quantity is not. A third and double are round numbers somebody picked, printed here so you can disagree. What they apply to comes from mintage figures already in this catalogue, each carrying the document it came from. An earlier version drew the line at five million on the reasoning that a coin becomes worth more than face value around there, which would have been the only number on this site traceable to nothing: where a premium begins is a fact about a market and no document states it. And a share of what was struck is not a share of what survives. A coin made in millions and then withdrawn and melted can be scarcer today than one made in thousands and hoarded, which is what the withdrawal and circulation records are for. A dot is a reading aid. It is not a valuation and it never becomes one.

Every Australian coin has a weight fixed by law, and no two denominations share one closely enough to confuse once you also look at the colour. A kitchen scale reading to a tenth of a gram settles it. These are the statutory weights, not measured averages, so a worn coin reads light.

The three near-collisions are deliberate. The florin and the twenty cents differ by 0.03 per cent, the shilling and the ten cents by 0.03, the sixpence and the five cents by 0.08. The decimal coins were struck to the weights of the ones they replaced so that machines built for one would take the other.

Marking a coin writes its id into this browser's own storage and nowhere else. There is no account here and no server to send it to, so it will not follow you to another device, and clearing your site data clears it. It is a convenience, not a record.