diff --git a/py/hexagram/thermo.py b/py/hexagram/thermo.py
index ea5f1f3..82e2259 100644
--- a/py/hexagram/thermo.py
+++ b/py/hexagram/thermo.py
@@ -36,9 +36,11 @@ class Thermometer(BottomDial):
         cr.set_line_width(6.0)
 
         level = self.min_value
-        incr  = math.ceil((self.max_value - self.min_value) / 9.0)
+        incr  = (self.max_value - self.min_value) / 9.0
+
+        for i in range(0, 9):
+            level = self.min_value + i * incr
 
-        while level <= self.max_value:
             if level >= self.WARN_VALUE:
                 cr.set_source_rgb(0.8, 0, 0)
             else: