From 8cdb4bd72bd4b705b5914310e3f1d6ad5f326b6c Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Mon, 1 Jun 2026 17:51:52 +0000
Subject: [PATCH] Fix FX rate convention to match market-standard quoting

Users were confused by the "X foreign = 1 local" convention, which is the
inverse of how exchange rates are normally quoted (e.g. "1 USD = 35 THB").
Flip to the market-standard "1 foreign = X local" direction, updating the
rate label, the price calculation (per * rate instead of per / rate), and
the PDF note.

Note: existing localStorage data using the old convention will produce
incorrect prices until users re-enter their exchange rates.

https://claude.ai/code/session_0151QtsUhzXmgzEhSvXG2SDt
---
 CLAUDE.md      |  2 +-
 app/config.yml |  8 ++++----
 app/index.html | 10 +++++-----
 3 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/CLAUDE.md b/CLAUDE.md
index b975b60..8410bf2 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -60,7 +60,7 @@ Do not break these behaviours:
 - **`addLine()` must `return i`** — `loadLines()` depends on the returned ID.
 - **`saveStorage()`** is triggered by `change` events on all `[data-ls]` elements; do not remove that listener.
 - **Invoice number bump:** occurs on the next page load after Generate via the `inv_generated_v1` flag; do not bump on Generate itself.
-- **FX rate convention:** X foreign units = 1 local unit. `price_local = price_foreign / exchange_rate`.
+- **FX rate convention:** 1 foreign unit = X local units (market-standard quote). `price_local = price_foreign * exchange_rate`.
 
 ## Config structure (`config.yml`)
 
diff --git a/app/config.yml b/app/config.yml
index aa7ff85..bd20241 100644
--- a/app/config.yml
+++ b/app/config.yml
@@ -360,10 +360,10 @@ translations:
     fr: Code devise
     "no": Valutakode
   exchange-rate:
-    en: "Exchange rate (X foreign = 1 local)"
-    de: "Wechselkurs (X Fremd = 1 Inland)"
-    fr: "Taux de change (X étranger = 1 local)"
-    "no": "Valutakurs (X utenlandsk = 1 lokal)"
+    en: "Exchange rate (1 foreign = X local)"
+    de: "Wechselkurs (1 Fremd = X Inland)"
+    fr: "Taux de change (1 étranger = X local)"
+    "no": "Valutakurs (1 utenlandsk = X lokal)"
   per-item:
     en: Price per item (foreign currency)
     de: Preis je Einheit (Fremdwährung)
diff --git a/app/index.html b/app/index.html
index 80121eb..5b4bd44 100644
--- a/app/index.html
+++ b/app/index.html
@@ -881,7 +881,7 @@ function toggleFx(i) {
           <select id="fcur-${i}" onchange="updateFxLabels(${i});calcLine(${i});saveLines()">${currOpts(defaultFcy)}</select>
         </div>
         <div>
-          <div class="fx-label" id="frate-lbl-${i}">Exchange rate (X ${h(defaultFcy)} = 1 ${h(lcy)})</div>
+          <div class="fx-label" id="frate-lbl-${i}">Exchange rate (1 ${h(defaultFcy)} = X ${h(lcy)})</div>
           <input type="number" id="frate-${i}" value="" min="0" step="any" oninput="calcFxFromPer(${i})">
         </div>
         <div>
@@ -900,7 +900,7 @@ function calcFxFromPer(i) {
   const per  = pn(document.getElementById(`fper-${i}`)?.value);
   const rate = pn(document.getElementById(`frate-${i}`)?.value) || 1;
   const prEl = document.getElementById(`price-${i}`);
-  if (prEl) prEl.value = (per / rate).toFixed(6);
+  if (prEl) prEl.value = (per * rate).toFixed(6);
   calcLine(i);
   saveLines();
 }
@@ -1327,7 +1327,7 @@ function buildPDF() {
     let   fxH     = 0;
     if (row.fxNote) {
       const fxStr = `${td("per-item")}: ${row.fxNote.cur} ${fmt(row.fxNote.per)} `
-                  + `(${(+row.fxNote.rate).toFixed(5)} ${row.fxNote.cur} = 1 ${iCur})`;
+                  + `(1 ${row.fxNote.cur} = ${(+row.fxNote.rate).toFixed(5)} ${iCur})`;
       const fxLines = sp(fxStr, CD + CP - 4);
       fxH = fxLines.length * 3.5 + 1;
     }
@@ -1360,7 +1360,7 @@ function buildPDF() {
 
     if (row.fxNote) {
       const fxStr = `${td("per-item")}: ${row.fxNote.cur} ${fmt(row.fxNote.per)} `
-                  + `(${(+row.fxNote.rate).toFixed(5)} ${row.fxNote.cur} = 1 ${iCur})`;
+                  + `(1 ${row.fxNote.cur} = ${(+row.fxNote.rate).toFixed(5)} ${iCur})`;
       fn(7); tc(107,114,128);
       const fxLines = sp(fxStr, CD + CP - 4);
       fxLines.forEach((fl, fi) => tL(fl, xD+2, y + ROW_H + descH + 3.2 + fi * 3.5));
@@ -1410,7 +1410,7 @@ function updateFxLabels(i) {
   const lcy = document.getElementById("icur")?.value || "";
   const rl = document.getElementById(`frate-lbl-${i}`);
   const pl = document.getElementById(`fper-lbl-${i}`);
-  if (rl) rl.textContent = `Exchange rate (X ${fcy} = 1 ${lcy})`;
+  if (rl) rl.textContent = `Exchange rate (1 ${fcy} = X ${lcy})`;
   if (pl) pl.textContent = `Price per item in ${fcy}`;
 }