diff --git a/src/msspec/iodata.py b/src/msspec/iodata.py
index 144bd03..27369d9 100644
--- a/src/msspec/iodata.py
+++ b/src/msspec/iodata.py
@@ -17,8 +17,8 @@
 # along with this msspec.  If not, see <http://www.gnu.org/licenses/>.
 #
 # Source file  : src/msspec/iodata.py
-# Last modified: Mon, 27 Sep 2021 17:49:48 +0200
-# Committed by : sylvain tricot <sylvain.tricot@univ-rennes1.fr>
+# Last modified: Mon, 11 Mar 2024 09:51:47 +0100
+# Committed by : Sylvain Tricot <sylvain.tricot@univ-rennes.fr>
 
 
 """
@@ -885,8 +885,10 @@ class _DataSetView(object):
                         R = np.sin(np.radians(theta))
                         R_ticks = np.sin(np.radians(theta_ticks))
                     elif proj == 'stereo':
-                        R = 2 * np.tan(np.radians(theta/2.))
-                        R_ticks = 2 * np.tan(np.radians(theta_ticks/2.))
+                        #R = 2 * np.tan(np.radians(theta/2.))
+                        #R_ticks = 2 * np.tan(np.radians(theta_ticks/2.))
+                        R = theta/90.
+                        R_ticks = theta_ticks/90.
                     #R = np.tan(np.radians(theta/2.))
                     X, Y = np.meshgrid(np.radians(phi), R)
                     im = axes.pcolormesh(X, Y, Xsec, shading='gouraud')