Deck calculator: make labels match the maths (burden, loaded rate, markup)

The arithmetic was already consistent, but three labels described something
other than what the code computes:
- "Overhead factor" multiplied labour only while a separate section held the
  real overhead, inviting double-counting -> "Labour burden (x)" + a hint.
- "Labor cost" showed wage x burden, i.e. the loaded rate, not a per-board
  cost -> "Loaded rate".
- "Profit margin (x)" was a markup -> "Markup (x)", with the implied gross
  margin % shown so the name matches the number.

Also: distinct board-count columns (Lifetime boards / Boards per order /
Boards per run) instead of three identical "# boards"; "Scrap / waste (%)".
PDF and Markdown exports use the same names. CSV machine keys are unchanged so
existing exports still round-trip.

AGENTS.md

@@ -819,7 +819,15 @@ session with **no other memory of this project**. So:
   calculator (2026-10-05):** the first in-app tool lives at `/diy/deck-cost`
   (`components/DeckCostCalculator.tsx`) — a self-contained (localStorage) model of
   labour, equipment amortisation, operations, materials, process time, packaging
-  and margin → selling price; the `deckCost` card links to it. **Currency
+  and margin → selling price; the `deckCost` card links to it. **Naming is
+  deliberate (2026-10-05):** the labour multiplier is **"Labour burden (×)"** (not
+  "overhead" — rent/bills are the separate **Operation expenses** section; the
+  hint warns against counting them twice), the derived `wage × burden` figure is
+  the **"Loaded rate"**, and the multiplier is **"Markup (×)"** with the implied
+  **gross margin %** shown (it is *not* a margin). The three `# boards` columns
+  are context-specific: **Lifetime boards** (equipment), **Boards / order**
+  (materials), **Boards / run** (processes). CSV keys stay machine-stable
+  (`overhead_factor`, `profit_margin`, …) for round-tripping. **Currency
   (2026-10-05):** a **searchable currency selector** (Popover + search) covering
   **sats + BTC** (both Bitcoin units) and every **fiat** Coinbase reports (crypto
   is filtered out via `FIAT_CODES`), and switching **converts every money field**

src/components/DeckCostCalculator.tsx

@@ -479,6 +479,9 @@ export function DeckCostCalculator() {
     };
   }, [s]);
 
+  /** Markup (×) expressed as a gross margin, so the name matches the maths. */
+  const marginPct = s.profitMargin > 0 ? Math.round((1 - 1 / s.profitMargin) * 100) : 0;
+
   const patch = (p: Partial<CalcState>) => setS((prev) => ({ ...prev, ...p }));
 
   const savePreset = () => {
@@ -554,8 +557,8 @@ export function DeckCostCalculator() {
 
     section('Labor');
     kv('Hourly rate', fmt(s.hourlyRate));
-    kv('Overhead factor', `${s.overheadFactor}\u00d7`);
-    kv('Labor cost', `${fmt(s.hourlyRate * s.overheadFactor)}/hr`);
+    kv('Labour burden', `${s.overheadFactor}\u00d7`);
+    kv('Loaded rate', `${fmt(s.hourlyRate * s.overheadFactor)}/hr`);
 
     section('Equipment');
     s.equipment.forEach((e) => {
@@ -589,8 +592,8 @@ export function DeckCostCalculator() {
     // ── Result (kept together) ──
     ensure(180);
     section('Result');
-    kv('Profit margin', `${s.profitMargin}\u00d7`);
-    kv('Scrap', `${s.scrapPct}%`);
+    kv('Markup', `${s.profitMargin}\u00d7  (\u2248 ${marginPct}% gross margin)`);
+    kv('Scrap / waste', `${s.scrapPct}%`);
     kv('Cost / board (no packaging)', fmt(r.costNoPack));
     kv('Cost / board (with packaging)', fmt(r.costWithPack));
     y += 6;
@@ -867,8 +870,8 @@ export function DeckCostCalculator() {
       '',
       '## Labor',
       `- Hourly rate: ${fmt(s.hourlyRate)}`,
-      `- Overhead factor: ${s.overheadFactor}×`,
-      `- Labor cost: ${fmt(s.hourlyRate * s.overheadFactor)}/hr`,
+      `- Labour burden: ${s.overheadFactor}×`,
+      `- Loaded rate: ${fmt(s.hourlyRate * s.overheadFactor)}/hr`,
       '',
       '## Equipment',
       ...s.equipment.map((e) => `- ${e.name}: ${fmt(e.boards > 0 ? (e.cost + e.setupHrs * r.laborPerHr) / e.boards : 0)} (${fmt(e.cost)} · ${e.boards.toLocaleString()} boards)`),
@@ -894,7 +897,7 @@ export function DeckCostCalculator() {
       `- **Packaging per board: ${fmt(r.packaging)}**`,
       '',
       '## Result',
-      `- Profit margin: ${s.profitMargin}× · Scrap: ${s.scrapPct}%`,
+      `- Markup: ${s.profitMargin}× (≈ ${marginPct}% gross margin) · Scrap: ${s.scrapPct}%`,
       `- Cost/board (no packaging): ${fmt(r.costNoPack)}`,
       `- Cost/board (with packaging): ${fmt(r.costWithPack)}`,
       `- **Selling price (no packaging): ${fmt(r.priceNoPack)}**`,
@@ -1043,16 +1046,17 @@ export function DeckCostCalculator() {
             {numInput(s.hourlyRate, (n) => patch({ hourlyRate: n }))}
           </label>
           <label className="space-y-1">
-            <span className={label}>Overhead factor (2–3)</span>
+            <span className={label}>Labour burden (×)</span>
             {numInput(s.overheadFactor, (n) => patch({ overheadFactor: n }))}
           </label>
           <div className="space-y-1">
-            <span className={label}>Labor cost</span>
+            <span className={label}>Loaded rate</span>
             <div className="flex h-8 items-center rounded-md border border-white/10 bg-black/40 px-2 text-sm font-bold text-[#ccff00]">
               {fmt(s.hourlyRate * s.overheadFactor)}/hr
             </div>
           </div>
         </div>
+        <p className="mt-2 text-[11px] text-gray-500">Loaded rate = wage × burden (employer taxes and insurance on labour). Rent and bills go under <span className="text-gray-300">Operation expenses</span> — don’t count them in both.</p>
       </section>
 
       {/* Equipment */}
@@ -1060,7 +1064,7 @@ export function DeckCostCalculator() {
         <h3 className="mb-2 text-sm font-black uppercase tracking-wide text-[#ccff00]">Equipment</h3>
         <div className="overflow-x-auto">
           <table className="w-full text-xs">
-            <thead><tr><th className={th}>Equipment</th><th className={th}>Cost ({unit})</th><th className={th}>Setup (h)</th><th className={th}># boards</th><th className={th}>Per board</th><th /></tr></thead>
+            <thead><tr><th className={th}>Equipment</th><th className={th}>Cost ({unit})</th><th className={th}>Setup (h)</th><th className={th}>Lifetime boards</th><th className={th}>Per board</th><th /></tr></thead>
             <tbody>
               {s.equipment.map((e) => (
                 <tr key={e.id} className="border-t border-white/5">
@@ -1098,7 +1102,7 @@ export function DeckCostCalculator() {
         <h3 className="mb-2 text-sm font-black uppercase tracking-wide text-[#ccff00]">Materials</h3>
         <div className="overflow-x-auto">
           <table className="w-full text-xs">
-            <thead><tr><th className={th}>Material</th><th className={th}>Order ({unit})</th><th className={th}>Ship ({unit})</th><th className={th}># boards</th><th className={th}>Order (m)</th><th className={th}>Unload (m)</th><th className={th}>Per board</th><th /></tr></thead>
+            <thead><tr><th className={th}>Material</th><th className={th}>Order ({unit})</th><th className={th}>Ship ({unit})</th><th className={th}>Boards / order</th><th className={th}>Order (m)</th><th className={th}>Unload (m)</th><th className={th}>Per board</th><th /></tr></thead>
             <tbody>
               {s.materials.map((m) => {
                 const per = m.boards > 0 ? (m.orderCost + m.shipping + (m.orderMin + m.unloadMin) * r.laborPerMin) / m.boards : 0;
@@ -1130,7 +1134,7 @@ export function DeckCostCalculator() {
         <h3 className="mb-2 text-sm font-black uppercase tracking-wide text-[#ccff00]">Process costs</h3>
         <div className="overflow-x-auto">
           <table className="w-full text-xs">
-            <thead><tr><th className={th}>Process</th><th className={th}>Time (m)</th><th className={th}># boards</th><th className={th}>Per board</th><th /></tr></thead>
+            <thead><tr><th className={th}>Process</th><th className={th}>Time (m)</th><th className={th}>Boards / run</th><th className={th}>Per board</th><th /></tr></thead>
             <tbody>
               {s.processes.map((p) => {
                 const per = p.boards > 0 ? (p.minutes * r.laborPerMin) / p.boards : 0;
@@ -1187,11 +1191,14 @@ export function DeckCostCalculator() {
       <section className="rounded-2xl border-2 border-[#ccff00]/30 bg-[#ccff00]/[0.04] p-4">
         <h3 className="mb-3 text-sm font-black uppercase tracking-wide text-[#ccff00]">Margins</h3>
         <div className="grid grid-cols-2 sm:grid-cols-4 gap-3">
-          <label className="space-y-1"><span className={label}>Profit margin (×)</span>{numInput(s.profitMargin, (n) => patch({ profitMargin: n }))}</label>
-          <label className="space-y-1"><span className={label}>Scrap (%)</span>{numInput(s.scrapPct, (n) => patch({ scrapPct: n }))}</label>
+          <label className="space-y-1"><span className={label}>Markup (×)</span>{numInput(s.profitMargin, (n) => patch({ profitMargin: n }))}</label>
+          <label className="space-y-1"><span className={label}>Scrap / waste (%)</span>{numInput(s.scrapPct, (n) => patch({ scrapPct: n }))}</label>
           <div className="space-y-1"><span className={label}>Cost / board (no packaging)</span><div className="flex h-8 items-center text-sm font-bold text-gray-200">{fmt(r.costNoPack)}</div></div>
           <div className="space-y-1"><span className={label}>Cost / board (with packaging)</span><div className="flex h-8 items-center text-sm font-bold text-gray-200">{fmt(r.costWithPack)}</div></div>
         </div>
+        <p className="mt-2 text-[11px] text-gray-500">
+          Markup {s.profitMargin}× ≈ <span className="text-gray-300">{marginPct}% gross margin</span> · waste {s.scrapPct}% is spread over the good boards.
+        </p>
 
         <div className="mt-4 grid grid-cols-1 sm:grid-cols-2 gap-3">
           <div className="rounded-xl border border-[#ccff00]/40 bg-black/40 p-3">