diff --git a/tests/test_interval.py b/tests/test_interval.py
index b207330..c55d724 100644
--- a/tests/test_interval.py
+++ b/tests/test_interval.py
@@ -325,24 +325,29 @@ class TestIntervalTree:
         render(iset, "In-order insertion")
 
 class TestIntervalSpeed:
-    @unittest.skip("this is slow")
+    #@unittest.skip("this is slow")
     def test_interval_speed(self):
         import yappi
         import time
         import aplotter
         import random
+        import math
 
         print
         yappi.start()
         speeds = {}
-        for j in [ 2**x for x in range(5,18) ]:
+        for j in [ 2**x for x in range(5,21) ]:
             start = time.time()
             iset = IntervalSet()
             for i in random.sample(xrange(j),j):
                 interval = Interval(i, i+1)
                 iset += interval
             speed = (time.time() - start) * 1000000.0
-            printf("%d: %g μs (%g μs each)\n", j, speed, speed/j)
+            printf("%d: %g μs (%g μs each, O(n log n) ratio %g)\n",
+                   j,
+                   speed,
+                   speed/j,
+                   speed / (j*math.log(j))) # should be constant
             speeds[j] = speed
         aplotter.plot(speeds.keys(), speeds.values(), plot_slope=True)
         yappi.stop()