diff --git a/README.md b/README.md
index aadd16b..73ff118 100644
--- a/README.md
+++ b/README.md
@@ -222,6 +222,7 @@ You may obtain a copy of the License at
 
 <p float="left">
   <img src="/images/image1.png" width=300 />
+  <img src="/images/image4.png" width=300 />
   <img src="/images/image2.png" width=300 />
   <img src="/images/image3.png" width=300 />
 </p>
diff --git a/images/image4.png b/images/image4.png
new file mode 100644
index 0000000..8e0a7e5
Binary files /dev/null and b/images/image4.png differ
diff --git a/ui/main.c b/ui/main.c
index 246fceb..c65e303 100644
--- a/ui/main.c
+++ b/ui/main.c
@@ -424,6 +424,7 @@ void big_freq(const uint32_t frequency, const unsigned int x, const unsigned int
 //		if (g_squelch_open)
 //			return;
 
+		// auto scale
 		max_rssi = g_panadapter_rssi[0];
 		min_rssi = g_panadapter_rssi[0];
 		for (i = 1; i < ARRAY_SIZE(g_panadapter_rssi); i++)
@@ -434,9 +435,8 @@ void big_freq(const uint32_t frequency, const unsigned int x, const unsigned int
 			if (min_rssi > rssi)
 				min_rssi = rssi;
 		}
-
 		span_rssi = max_rssi - min_rssi;
-		if (span_rssi < 40)  // minimum vertical range
+		if (span_rssi < 40)  // minimum vertical range (20dB)
 		{
 			span_rssi = 40;
 			if (min_rssi > (255 - span_rssi))
@@ -449,7 +449,7 @@ void big_freq(const uint32_t frequency, const unsigned int x, const unsigned int
 			memset(g_frame_buffer[line], 0, LCD_WIDTH * 3);
 		}
 
-		// draw the bins
+		// draw the vertical bins
 		for (i = 0; i < ARRAY_SIZE(g_panadapter_rssi); i++)
 		{
 			uint8_t  rssi = g_panadapter_rssi[i];
@@ -459,7 +459,7 @@ void big_freq(const uint32_t frequency, const unsigned int x, const unsigned int
 				rssi = (rssi < ((-129 + 160) * 2)) ? 0 : rssi - ((-129 + 160) * 2);  // min of -129dBm (S3)
 				rssi = rssi >> 2;
 			#else
-				rssi = ((rssi - min_rssi) * 22) / span_rssi;  // 0 ~ 21
+				rssi = ((rssi - min_rssi) * 20) / span_rssi;  // 0 ~ 20
 			#endif
 
 			rssi += 2;