diff --git a/test/runtests.jl b/test/runtests.jl
index cf4200e..6b69f92 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -8,6 +8,7 @@ using MeshIO
 using LinearAlgebra
 
 @testset "simple cube stl" begin
+    # https://hepweb.ucsd.edu/ph110b/110b_notes/node26.html
     stl = load(raw"test\test_assets\cubeblender.stl")
 
     props = get_mass_properties(stl)