diff --git a/ui/src/components/OperationPanel.jsx b/ui/src/components/OperationPanel.jsx
index 7bf8172..a498961 100644
--- a/ui/src/components/OperationPanel.jsx
+++ b/ui/src/components/OperationPanel.jsx
@@ -258,6 +258,12 @@ function derive(current, edit, dp = 2) {
     new:    fmtNum(next,   dp),
     change: fmtNum(change, dp),
     pct:    pct == null ? '—' : fmtNum(pct, 1),
+    // The same three as numbers, for anything that needs to compute with them.
+    // The strings above are grouped by toLocaleString, and parseFloat stops at
+    // the first separator -- "3,456,789" reads back as 3 -- so a caller that
+    // re-parsed the display got a plausible small number rather than an error.
+    // Nothing should have to know that; the numbers travel alongside.
+    n: { new: next, change, pct },
   }
   out[edit.field] = edit.raw        // keep what you typed exactly as typed
   return out
@@ -442,9 +448,8 @@ function ScaleLedger({ currentTotals, scaleInputs, setScaleInputs, scalePlug, se
   // left units and price blank -- exactly the two numbers you need to see to
   // know whether you asked for a price change or a volume change.
   const numOf = (key, field) => {
-    const raw = derived[key]?.[field]
-    const n = parseFloat(raw)
-    return isFinite(n) ? n : null
+    const n = derived[key]?.n?.[field]
+    return n != null && isFinite(n) ? n : null
   }
 
   const outcome = (() => {