diff --git a/lib/xmet/skew_t.py b/lib/xmet/skew_t.py
index b73f566..8d66026 100644
--- a/lib/xmet/skew_t.py
+++ b/lib/xmet/skew_t.py
@@ -104,12 +104,12 @@ class SkewT():
             # Temperature may possibly be dewpoint, depending on the
             # return value of the callback.
             #
-            temp, pressure = fn(sample)
+            temp = fn(sample)
 
             if temp is None:
                 continue
 
-            gx, gy = self.sample_to_graph(temp, pressure)
+            gx, gy = self.sample_to_graph(temp, sample.pressure)
             sx, sy = self.graph_to_screen(gx, gy)
 
             if first:
@@ -129,7 +129,7 @@ class SkewT():
         self.draw_isobars(cr, x, y)
 
         cr.set_source_rgb(1, 0, 0)
-        self.draw_samples(cr, x, y, samples, lambda s: (s.temp, s.pressure))
+        self.draw_samples(cr, x, y, samples, lambda s: s.temp)
 
         cr.set_source_rgb(0, 1, 0)
-        self.draw_samples(cr, x, y, samples, lambda s: (s.dewpoint, s.pressure))
+        self.draw_samples(cr, x, y, samples, lambda s: s.dewpoint)