diff --git a/README.md b/README.md
index e2e4d83c..53619638 100644
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+++ b/README.md
@@ -140,6 +140,10 @@ Ref:
 
 This is a 2D localization example with Histogram filter.
 
+The red cross is true position, black points are RFID positions.
+
+The blue grid shows a position probability of histogram filter.  
+
 In this simulation, x,y are unknown, yaw is known.
 
 The filter integrates speed input and range observations from RFID for localization.