diff --git a/index.html b/index.html
index f43d0eb..66b8733 100644
--- a/index.html
+++ b/index.html
@@ -293,8 +293,7 @@ <h2>NPF Rule Calculator</h2>
                 href="https://sahavre.fr/wp/regle-npf-rule/">https://sahavre.fr/wp/regle-npf-rule/</a></p>
             <h2>Simplified NPF Rule Calculator</h2>
             <code>Shutter Speed = (35 * Lens Aperture + 30 * Pixel Size) / Focal Length</code>
-            <p>A Simplified version of the original NPF rule that does not take into account the pixel density of the
-              camera sensor.</p>
+            <p>A Simplified version of the original NPF rule that uses a rough formula which uses a declination of 60° instead of 0° and does not take into account the (small) effect of the seeing. </p>
             <p class="source">Michaud, F. (2020, December 1). La Règle NPF – Société Astronomique du Havre. sahavre.fr.
               Retrieved August 12, 2022, from <a
                 href="https://sahavre.fr/wp/regle-npf-rule/">https://sahavre.fr/wp/regle-npf-rule/</a></p>
@@ -350,4 +349,4 @@ <h2>The 4 Crop Rule Calculation</h2>
   </footer>
 </body>
 
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+</html>