diff --git a/index.html b/index.html
index 048aab9..e6c5e7c 100644
--- a/index.html
+++ b/index.html
@@ -257,7 +257,8 @@ <h3>Sampling and Reporting Rate</h3>
     <ul>
       <li>
         <dfn data-dfn-for="pressure source sample">data</dfn>: [=contributing
-        factors=] obtained from the underlying hardware or operating system.
+        factors=] obtained from the underlying hardware or operating system or,
+        in the case of a [=virtual pressure source=], a {{PressureState}}.
       </li>
       <li>
         <dfn data-dfn-for="pressure source sample">timestamp</dfn>: the