diff --git a/neutronpy/instrument.py b/neutronpy/instrument.py
index 74bf662..7ae033f 100644
--- a/neutronpy/instrument.py
+++ b/neutronpy/instrument.py
@@ -1057,6 +1057,12 @@ def calc_resolution_in_Q_coords(self, Q, W):
             else:
                 s2theta = np.real(s2theta)
 
+            # correct sign of curvatures
+            monorh = monorh * sm
+            monorv = monorv * sm
+            anarh = anarh * sa
+            anarv = anarv * sa
+
             thetas = s2theta / 2.
             phi = np.arctan2(-kf * np.sin(s2theta), ki - kf * np.cos(s2theta))
 
diff --git a/neutronpy/instrument_tools.py b/neutronpy/instrument_tools.py
index 9c62823..77e1464 100644
--- a/neutronpy/instrument_tools.py
+++ b/neutronpy/instrument_tools.py
@@ -74,13 +74,13 @@ def ellipse(saxis1, saxis2, phi=0, origin=None, npts=31):
 
 
 def get_bragg_widths(RM):
-    bragg = [np.sqrt(8 * np.log(2)) / np.sqrt(RM[0, 0]),
-             np.sqrt(8 * np.log(2)) / np.sqrt(RM[1, 1]),
-             np.sqrt(8 * np.log(2)) / np.sqrt(RM[2, 2]),
-             get_phonon_width(0, RM, [0, 0, 0, 1])[1],
-             np.sqrt(8 * np.log(2)) / np.sqrt(RM[3, 3])]
+    bragg = np.array([np.sqrt(8 * np.log(2)) / np.sqrt(RM[0, 0]),
+                      np.sqrt(8 * np.log(2)) / np.sqrt(RM[1, 1]),
+                      np.sqrt(8 * np.log(2)) / np.sqrt(RM[2, 2]),
+                      get_phonon_width(0, RM, [0, 0, 0, 1])[1],
+                      np.sqrt(8 * np.log(2)) / np.sqrt(RM[3, 3])])
 
-    return bragg
+    return bragg * 2
 
 
 def get_phonon_width(r0, M, C):
diff --git a/tests/test_resolution.py b/tests/test_resolution.py
index 8bbf852..9389fe4 100644
--- a/tests/test_resolution.py
+++ b/tests/test_resolution.py
@@ -195,7 +195,7 @@ def test_cooper_nathans(self):
         NP = EXP.RMS
         R = EXP.R0
         BraggWidths = get_bragg_widths(NP)
-        angles = self.EXP_popovici.get_angles_and_Q(hkle)[0]
+        angles = self.EXP_coopernathans.get_angles_and_Q(hkle)[0]
         ResVol = (2 * np.pi) ** 2 / np.sqrt(np.linalg.det(NP)) * 2
 
         self.assertTrue(np.all(np.abs((RMS - NP)) < 100))