diff --git a/doc/user_guide/en/controls-functions-left.adoc b/doc/user_guide/en/controls-functions-left.adoc
index c380daec8..fb3250495 100644
--- a/doc/user_guide/en/controls-functions-left.adoc
+++ b/doc/user_guide/en/controls-functions-left.adoc
@@ -34,6 +34,10 @@ split transmit frequency. When using _WSJT-X_ with such radios you
 should not change the current VFO, split status or dial frequency
 using controls on the radio.
 
+* The slider adjacent to the level meter can be used to adjust the
+signal level sent to the Fast Graph.  If *Flatten* is not checked,
+the same is true for the Wide Graph.
+
 * If *DX Grid* contains a valid Maidenhead locator, the corresponding
 great-circle azimuth and distance from your location are displayed.