diff --git a/templates/index.html.ep b/templates/index.html.ep
index dda695d..b9dae8a 100644
--- a/templates/index.html.ep
+++ b/templates/index.html.ep
@@ -961,7 +961,7 @@
                     <th id="dice_tt">dice</th>
                     <th id="logdice_tt">LD</th>
                     <th id="logdiceaf_tt">LDaf</th>
-                    <th id="delta_tt" title="Delta to log-Dice score in reference corpus.">Δ</th>
+                    <th id="delta_tt" title="Delta to log-Dice score in reference corpus. ⚠: If the collocate is not within the top 200 of the reference corpus, a reference value of min(lD)-0.1 is assumed.">Δ</th>
                     <th id="af_win" title="Positions around the target word that are selected by the auto-focus function are marked with ◾. Positions at which the collocate appears at least once are marked with ◽.">af-window</th>
                     <th title="PMI³ restricted to left neighbour">l-PMI³</th>
                     <th title="PMI³ restricted to right neighbour">r-PMI³</th>