diff --git a/sdrgui/readme.md b/sdrgui/readme.md
index 5a56fa4e3..10f0cc163 100644
--- a/sdrgui/readme.md
+++ b/sdrgui/readme.md
@@ -288,7 +288,7 @@ When phosphor display is engaged (4.C) and stroke decay is 1 (4.7) this divides
 
 <h4>4.9. Phosphor display stroke strength</h4>
 
-This controls the stroke strength when phosphor display is engaged (4.C).
+This controls the stroke strength when phosphor display is engaged (4.C). The histogram value is incremented by this value at each new FFT until the maximum (red) is reached.
 
 <h4>4.A. Trace intensity</h4>