diff --git a/apps/metro/readme.txt b/apps/metro/readme.txt
index 0195cdbb..02bfc2bf 100644
--- a/apps/metro/readme.txt
+++ b/apps/metro/readme.txt
@@ -85,7 +85,8 @@ where "file1" and "file2" are the input meshes in PLY, OFF or STL format, and op
   -H         Use an Hashed Uniform Grid as Search Structure
   
   
-The -C option is useful for creating a set of meshes with a coherent coloring scheme. 
+The -C option is useful in combination with -c option for creating a set of 
+meshes with a coherent coloring scheme. 
 It sets how the errors are mapped into color according to the following formula, 
 let e be the error and ColorRamp be a R->RGB function mapping 0..1 values 
 into a smooth RedYellowGreenCyanBlue ramp:
@@ -93,3 +94,6 @@ into a smooth RedYellowGreenCyanBlue ramp:
 			e=Clamp(e,min,max);
 			VertexColor = ColorRamp( (e-min)/(max-min) );
 
+The Histogram files saved by the -h option contains two column of numbers 
+e_i and p_i; p_i denotes the fraction of the surface having an error 
+between e_i and e_{i+1}. The sum of the second column values should give 1.
\ No newline at end of file