diff --git a/examples/poly-spline/src/index.ts b/examples/poly-spline/src/index.ts
index 9ecb30d0d2..f1f88c686a 100644
--- a/examples/poly-spline/src/index.ts
+++ b/examples/poly-spline/src/index.ts
@@ -82,6 +82,7 @@ const app = (
     _uniScale: Stream<number>
 ) => ({ poly, mode, uniform, scale, uniScale }: any) => {
     // reconstruct poly as cubic curve segments
+    // reference: https://github.com/thi-ng/umbrella/tree/develop/packages/geom-splines#polygon-to-cubic-curve-conversion
     const cubics = asCubic(poly, {
         breakPoints: mode,
         scale: scale * (uniform ? uniScale : 1),