diff --git a/27-IBL-With-Material-Texture/Shader/0-2 GRS_PBR_Function.hlsli b/27-IBL-With-Material-Texture/Shader/0-2 GRS_PBR_Function.hlsli
index 6ca6b8b33bd62d2dcd162ae3ad5f94032437fd86..178256a67030128a34fbed09fe694028a55edea1 100644
--- a/27-IBL-With-Material-Texture/Shader/0-2 GRS_PBR_Function.hlsli	
+++ b/27-IBL-With-Material-Texture/Shader/0-2 GRS_PBR_Function.hlsli	
@@ -43,9 +43,9 @@ float2 SampleSphericalMap(float3 coord)
 	float theta = acos(coord.y);
 	float phi = atan2(coord.x, coord.z);
 	phi += (phi < 0) ? 2 * PI : 0;
-
-	float u = phi * 0.1591f;
-	float v = theta * 0.3183f;
+	// to [0,1]
+	float u = phi	* INV_TWO_PI;
+	float v = theta * INV_PI;
 	return float2(u, v);
 }