diff --git a/handbook/l/new-cave-form.html b/handbook/l/new-cave-form.html
index 1c3fe9d1b..c253f12d1 100644
--- a/handbook/l/new-cave-form.html
+++ b/handbook/l/new-cave-form.html
@@ -55,6 +55,9 @@ href="/expofiles/documents/surveying/newcavedatasheet.pdf">here</a>.
 <li>You can download a master copy of the sheet <a 
 href="/expofiles/documents/surveying/newcavedatasheet.odt">here</a>.
 
+  <h4>Why we ask for the time</h4>
+<p>GPS readings sometimes go walkabout during a period of ionospheric disturbance (an hour or so, which happen several times a day)  or whenever there is a Russian invasion. We intend to keep a continuous record of GPS at basecamp so that we can identify these periods where GPS records are not to be trusted.
+ 
 </ul>
 <h4>Historic Prospecting Form</h3>
 <p>We used to have a Prospecting Form: <br>