imporve howto
@@ -45,9 +45,11 @@ You can also select observations based on other informations available using the
`~gammapy.data.ObservationTable.select_observations` method.
Make a on-axis equivalent livetime map
-+++++++++++++++++++
+++++++++++++++++++++++++++++++++++++++
-To compute an effective on-axis exposure in hours, see `here
+IACT detection efficiency varies in the FoV. To have an estimate
+of the effective exposure with respect to the on-axis one,
+it can be useful to build an `on-axis equivalent lifetime map
<tutorials/data/hess.html#On-axis-equivalent-livetime>`__.
