diff --git a/ViewGraph.tsx b/ViewGraph.tsx
index e5516a1..ef83df2 100644
--- a/ViewGraph.tsx
+++ b/ViewGraph.tsx
@@ -26,9 +26,11 @@ export default function ViewGraph() {
   const [unit, setUnit] = useState('kg');
 
   const convertWeight = (weight: number, unitFrom: string, unitTo: string) => {
-    if (unitFrom === unitTo) return weight;
-    if (unitFrom === 'lb' && unitTo === 'kg') return weight * 0.453592;
-    if (unitFrom === 'kg' && unitTo === 'lb') return weight * 2.20462;
+    let result = weight;
+    if (unitFrom === unitTo) result = weight;
+    if (unitFrom === 'lb' && unitTo === 'kg') result = weight * 0.453592;
+    if (unitFrom === 'kg' && unitTo === 'lb') result = weight * 2.20462;
+    return isNaN(result) ? 0 : result;
   };
 
   useEffect(() => {