diff --git a/openrtx/src/ui.c b/openrtx/src/ui.c
index ef7ceae7..987487ca 100644
--- a/openrtx/src/ui.c
+++ b/openrtx/src/ui.c
@@ -17,6 +17,43 @@
  *   along with this program; if not, see <http://www.gnu.org/licenses/>   *
  ***************************************************************************/
 
+/*
+ * The graphical user interface (GUI) works by splitting the screen in 
+ * horizontal rows, with row height depending on vertical resolution.
+ * 
+ * The general screen layout is composed by an upper status bar at the
+ * top of the screen and a lower status bar at the bottom.
+ * The central portion of the screen is filled by two big text/number rows
+ * And a small row.
+ *
+ * Below is shown the row height for two common display densities.
+ *
+ *        160x128 display (MD380)
+ *      ┌─────────────────────────┐
+ *      │  top_status_bar (16px)  │
+ *      ├─────────────────────────┤
+ *      │      Line 1 (32px)      │
+ *      │                         │
+ *      │      Line 2 (32px)      │
+ *      │                         │
+ *      │      Line 3 (32px)      │
+ *      │                         │
+ *      ├─────────────────────────┤
+ *      │bottom_status_bar (16px) │
+ *      └─────────────────────────┘
+ *
+ *         128x64 display (GD77)
+ *      ┌─────────────────────────┐
+ *      │  top_status_bar (8px)   │
+ *      ├─────────────────────────┤
+ *      │      Line 1 (16px)      │
+ *      │      Line 2 (16px)      │
+ *      │      Line 3 (16px)      │
+ *      ├─────────────────────────┤
+ *      │ bottom_status_bar (8px) │
+ *      └─────────────────────────┘
+ */
+
 #include <stdio.h>
 #include <ui.h>