Multi-currency — Rows keep theirs, totals convert

Only aggregates convert. A £250 deal reads £250 in its row, to everybody, forever — restating it as $317 in the row would have the product assert an amount nobody agreed to. But adding £250 to $300 and printing 550 is worse than either, because a total of unlike currencies is not a number at all. So the rows keep their own currency and the total is converted, which is the one place a common currency is genuinely required. The grid's summary row, reports, dashboard tiles and every computed column go through the same conversion, so none of them can answer the same question differently. Amounts are decimal and numeric(28,12) throughout, and a set of amounts is summed at full precision and rounded once — rounding each line and then adding compounds an error that stays invisible until somebody reconciles against their books, which is exactly when it matters. Only a money column is treated as money. A Number field that happens to contain a price is a number, and converting it would be the product deciding what your data means.