diff --git a/Examples/Tests/gaussian_beam/analysis_focusing_beam.py b/Examples/Tests/gaussian_beam/analysis_focusing_beam.py
index c97c9d42658..e570e84e5fc 100755
--- a/Examples/Tests/gaussian_beam/analysis_focusing_beam.py
+++ b/Examples/Tests/gaussian_beam/analysis_focusing_beam.py
@@ -57,6 +57,7 @@ def s(z, sigma0, emit):
         sx.append(np.sqrt(np.average((x[i]-mux)**2, weights=w[i])))
         sy.append(np.sqrt(np.average((y[i]-muy)**2, weights=w[i])))
 
+# Theoretical prediction for the size of the beam in each z slice
 sx_theory = s(subgrid, sigmax, emitx/gamma)
 sy_theory = s(subgrid, sigmay, emity/gamma)