diff --git a/docs/research/Tribology_Storage_Evaluation.html b/docs/research/Tribology_Storage_Evaluation.html
index 83f8f46..8151972 100644
--- a/docs/research/Tribology_Storage_Evaluation.html
+++ b/docs/research/Tribology_Storage_Evaluation.html
@@ -615,8 +615,10 @@ function tabs(containerId, items, onPick){
 }
 
 /* ---------- navigation ---------- */
-const navLinks = document.querySelectorAll("nav.side a");
+/* menu items only: the sidebar footer also holds a regular external link */
+const navLinks = document.querySelectorAll('nav.side a[href^="#"]');
 function show(id){
+  if(!document.getElementById(id)) return;
   document.querySelectorAll("main section").forEach(s => s.classList.toggle("on", s.id === id));
   navLinks.forEach(a => a.classList.toggle("active", a.getAttribute("href") === "#" + id));
   el("main").scrollTop = 0;