a seriesThe dated exchange rate table

One set of exchange rates, fetched once and stamped, so prices published in twenty-odd currencies can sit on a single axis. The copy on disk holds 166 currencies against the US dollar, rates dated Wednesday 16 September 2026, fetched the same day from the open endpoint of ExchangeRate-API.

A price on this site keeps the currency it was published in. The dollar figure beside it is this table applied, and it moves whenever the table is refetched — so a page can change its dollar column without a hospital changing its price.

That is not a rounding problem. A Turkish package quoted at 60,000 lira in 2019 and the same 60,000 lira today are different amounts of money to a foreign buyer; converting an old price at a new rate reports something nobody paid. Two dates therefore travel with every converted figure on this site: the date the price was published and the date of the rate.

Inference — the rate is also not the price of a transaction. A patient pays a card rate, an interbank rate plus a spread, a foreign-transaction fee, or a currency conversion offered at the terminal, and the difference between the mid-market rate in this table and what leaves an account can run to several per cent on a five-figure bill. This site converts at mid-market because it is a stated, dated, reproducible number, not because it is what anybody was charged.

tools/fetch_rates.py reads https://open.er-api.com/v6/latest/USD, keeps every positive numeric rate, and stores them with the provider's own time_last_update_utc as the rate date. A currency the table does not carry leaves its price unconverted, and the page prints it in its own currency. tools/build.py computes the usd field on every price row from this table; a usd figure typed by hand into a record is overwritten.

The open endpoint updates once a day and requires attribution to ExchangeRate-API on any page that uses the rates; its terms do not permit redistributing the rate data itself.