Why a euro coin is never worth less than a euro
Price guides quote euro coins in dollars, and the exchange rate sometimes puts the quote under the coin's own face value. A coin you can spend is worth what it spends.
In the Buck index
Italy 2 euroItaly · 2002–2007 · Bimetallic: nickel brass clad nickel centre in copper-nickel ring$2.34 to $4.67
Spain 2 euroSpain · 1999–2006 · Bimetallic: nickel brass clad nickel centre in copper-nickel ring$2.34 to $3.74
Here is a small absurdity that shows up in every coin price database, ours included until we fixed it.
A twenty-cent euro coin has a face value of about $0.23. It is legal tender: you can walk into any shop in the eurozone and it will be accepted at twenty cents, today, without argument. And yet the price guide for that coin, quoted in US dollars and converted at a rate that moved since the figure was set, sometimes says $0.22.
At that point an app has a choice. It can print $0.22, which is what the data says. Or it can notice that the number is nonsense and refuse to print it.
The floor
We take the second option. A record that is current, circulating, legal-tender cash gets its low and its high clamped at face value, converted at the live rate. If the guide says less, the guide loses.
The rule is narrow on purpose. It fires only when the coin is one of the eight circulating euro denominations, and never when a record is marked demonetised. A 1943 Italian five-centesimi piece must not be floored at five euro cents; the lira has not been money since 2002 and the coin's worth is entirely collector worth.
Extending the same idea to other currencies, a current British 50p or a Polish five złoty, needs the same demonetisation awareness first. That is a data question, not a regular expression, and it is why the floor is still euro-only.
The mirror of the same problem
The floor has a twin, and the twin was worse.
Most published price data for modern coins quotes them in uncirculated condition: a coin that has never been in a pocket, never touched another coin, and still carries its mint lustre. That figure can be an order of magnitude above what the coin in your hand is worth, because the coin in your hand has been in a pocket.
For a euro coin the gap is comic. A French two-euro piece is worth two euros. Its uncirculated median in a price guide can read fifteen dollars and change, and for a while that is exactly what we showed people, on 44% of all euro scans.
So the same gate does a second job: when the only figure available is a mint-state one and the coin is current circulating cash, the range becomes face value to the uncirculated figure, and the label goes back to "estimated value" instead of claiming a grade. The number stops being a promise your pocket change is flawless and starts being what it always was, a band.
Why bother
Because the alternative is an app that tells everybody their change is treasure, and the day it says a coin is worth two dollars nobody believes it either.
A valuation is a claim. If the claim is only credible when it is flattering, it is not a valuation, it is a slot machine.
