diff --git a/crpptbx/TCV/gdat_tcv.m b/crpptbx/TCV/gdat_tcv.m
index 729b45ef00e3d8430afb94354a8d88fbd821476c..6fc82f4bc579d6f4d49508a121cf520085e4fca8 100644
--- a/crpptbx/TCV/gdat_tcv.m
+++ b/crpptbx/TCV/gdat_tcv.m
@@ -1289,7 +1289,7 @@ elseif strcmp(mapping_for_tcv.method,'switchcase')
     rhopol_eff(:) = sqrt(linspace(0,1,length(tracetdi.dim{1})));
     gdat_data.dim{1} = rhopol_eff;
     gdat_data.x = gdat_data.dim{1};
-    gdat_data.dimunits{1} = '';
+    gdat_data.dimunits{1} = 'rho_pol~sqrt(\psi_norm)';
     gdat_data.dimunits{2} = 's';
     gdat_data.units = '';
     gdat_data.request_description = 'q(rhopol\_norm)';