diff --git a/src/grove/grove.cxx b/src/grove/grove.cxx
index 955a0567..bd8b5385 100644
--- a/src/grove/grove.cxx
+++ b/src/grove/grove.cxx
@@ -79,8 +79,9 @@ GroveTemp::~GroveTemp()
 int GroveTemp::value ()
 {
     int a = mraa_aio_read(m_aio);
+    a = a >> 2;
     float r = (float)(1023-a)*10000/a;
-    float t = 1/(logf(r/10000)/3975 + 1/298.15)-273.15;
+    float t = 1/(log(r/10000)/3975 + 1/298.15)-273.15;
     return (int) t;
 }