diff --git a/lib/xmet/skew_t.py b/lib/xmet/skew_t.py
index 153bf28..58e0f48 100644
--- a/lib/xmet/skew_t.py
+++ b/lib/xmet/skew_t.py
@@ -49,21 +49,27 @@ class SkewTGraph():
 
         return factor * self.height
 
+    def draw_isobar(self, cr: cairo.Context,
+                    x: float,
+                    y: float,
+                    pressure: float):
+        sx, sy = self.graph_to_screen(-self.width / 2,
+                                      self.pressure_to_y(pressure))
+
+        cr.move_to(x + sx, y + sy)
+        cr.rel_line_to(self.width, 0)
+        cr.stroke()
+
     def draw_isobars(self, cr: cairo.Context, x: float, y: float):
         cr.save()
 
         cr.set_source_rgb(0.75, 0.75, 0.75)
 
         for pressure in range(PRESSURE_MIN, PRESSURE_MAX+1, PRESSURE_STEP):
-            coords = self.graph_to_screen(-self.width / 2,
-                                         self.pressure_to_y(pressure))
-
             if pressure % (2*PRESSURE_STEP) != 0:
                 continue
 
-            cr.move_to(x + coords[0], y + coords[1])
-            cr.rel_line_to(self.width, 0)
-            cr.stroke()
+            self.draw_isobar(cr, x, y, pressure)
 
         cr.restore()