diff --git a/openmc/cell.py b/openmc/cell.py
index e83d01dcd..b578702bb 100644
--- a/openmc/cell.py
+++ b/openmc/cell.py
@@ -99,6 +99,7 @@ class Cell(object):
         self.fill = fill
         self.region = region
         self._rotation = None
+        self._rotation_matrix = None
         self._temperature = None
         self._translation = None
         self._paths = []
@@ -196,14 +197,7 @@ class Cell(object):
 
     @property
     def rotation_matrix(self):
-        if self.rotation is not None:
-            phi, theta, psi = self.rotation*(-pi/180.)
-            c3, s3 = cos(phi), sin(phi)
-            c2, s2 = cos(theta), sin(theta)
-            c1, s1 = cos(psi), sin(psi)
-            return np.array([[c1*c2, c1*s2*s3 - c3*s1, s1*s3 + c1*c3*s2],
-                             [c2*s1, c1*c3 + s1*s2*s3, c3*s1*s2 - c1*s3],
-                             [-s2, c2*s3, c2*c3]])
+        return self._rotation_matrix
 
     @property
     def temperature(self):
@@ -288,6 +282,17 @@ class Cell(object):
         cv.check_length('cell rotation', rotation, 3)
         self._rotation = np.asarray(rotation)
 
+        # Save rotation matrix -- the reason we do this instead of having it be
+        # automatically calculated when the rotation_matrix property is accessed
+        # is so that plotting on a rotated geometry can be done faster.
+        phi, theta, psi = self.rotation*(-pi/180.)
+        c3, s3 = cos(phi), sin(phi)
+        c2, s2 = cos(theta), sin(theta)
+        c1, s1 = cos(psi), sin(psi)
+        return np.array([[c1*c2, c1*s2*s3 - c3*s1, s1*s3 + c1*c3*s2],
+                         [c2*s1, c1*c3 + s1*s2*s3, c3*s1*s2 - c1*s3],
+                         [-s2, c2*s3, c2*c3]])
+
     @translation.setter
     def translation(self, translation):
         cv.check_type('cell translation', translation, Iterable, Real)
diff --git a/openmc/executor.py b/openmc/executor.py
index 518153512..51215e8b7 100644
--- a/openmc/executor.py
+++ b/openmc/executor.py
@@ -48,6 +48,10 @@ def plot_geometry(output=True, openmc_exec='openmc', cwd='.'):
 def plot_inline(plots, openmc_exec='openmc', cwd='.', convert_exec='convert'):
     """Display plots inline in a Jupyter notebook.
 
+    This function requires that you have a program installed to convert PPM
+    files to PNG files. Typically, that would be `ImageMagick
+    <https://www.imagemagick.org>`_ which includes a `convert` command.
+
     Parameters
     ----------
     plots : Iterable of openmc.Plot
diff --git a/openmc/plots.py b/openmc/plots.py
index d95bc5905..2ba5d9758 100644
--- a/openmc/plots.py
+++ b/openmc/plots.py
@@ -483,8 +483,8 @@ class Plot(object):
             The basis directions for the plot
         slice_coord : float
             The level at which the slice plot should be plotted. For example, if
-            the basis is 'xy', this would indicate at what z value is used in
-            the origin.
+            the basis is 'xy', this would indicate the z value used in the
+            origin.
 
         """
         cv.check_type('geometry', geometry, openmc.Geometry)
@@ -565,7 +565,7 @@ class Plot(object):
         seed : int
             The random number seed used to generate the color scheme
         alpha : float
-            The value to apply in alpha compisiting
+            The value between 0 and 1 to apply in alpha compisiting
         background : 3-tuple of int or str
             The background color to apply in alpha compisiting
 
@@ -794,7 +794,7 @@ class Plots(cv.CheckedList):
         seed : int
             The random number seed used to generate the color scheme
         alpha : float
-            The value to apply in alpha compisiting
+            The value between 0 and 1 to apply in alpha compisiting
         background : 3-tuple of int or str
             The background color to apply in alpha compisiting