diff --git a/ImageD11/grain.py b/ImageD11/grain.py
index 3ea6b52c..9d1592d2 100644
--- a/ImageD11/grain.py
+++ b/ImageD11/grain.py
@@ -59,6 +59,7 @@ def __init__(self,ubi,translation=None, **kwds):
     def set_ubi(self, ubi):
         """ Update the orientation and clear cached values """
         self.ubi = np.array(ubi,float)
+        assert np.linalg.det(self.ubi) >= 0, 'Left handed axis system!'
         self.clear_cache()        
 
     def clear_cache(self):
diff --git a/scripts/refine_em.py b/scripts/refine_em.py
index 4b977fd9..1bc3404a 100644
--- a/scripts/refine_em.py
+++ b/scripts/refine_em.py
@@ -39,8 +39,12 @@ def setup():
 
 if __name__=="__main__":
     cmds  = setup()
-#    sys.exit()
-    p = multiprocessing.Pool( multiprocessing.cpu_count() )
+    
+    if 'SLURM_CPUS_PER_TASK' in os.environ:
+        njobs = int(os.environ['SLURM_CPUS_PER_TASK'])
+    else:
+        njobs =  multiprocessing.cpu_count()
+    p = multiprocessing.Pool( njobs )
     p.map( os.system, cmds )
     sys.exit()
     for c in cmds:
diff --git a/setup.cfg b/setup.cfg
index 3939c905..685039fc 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -1,2 +1,2 @@
 [tool:pytest]
-norecursedirs = ImageD11/depreciated
+norecursedirs = ImageD11/depreciated .ipynb_checkpoints