Index: branches/eam_branches/relphot.20200519/src/args.c
===================================================================
--- branches/eam_branches/relphot.20200519/src/args.c	(revision 41360)
+++ branches/eam_branches/relphot.20200519/src/args.c	(revision 41362)
@@ -315,4 +315,13 @@
       exit (2);
     }
+  }
+
+  // calibrate the photometry by night / time period
+  TGROUP_ZEROPT = FALSE;
+  if ((N = get_argument (argc, argv, "-tgroup"))) {
+    TGROUP_ZEROPT = TRUE;
+    remove_argument (N, &argc, argv);
+    loadTGroups (argv[N]);
+    remove_argument (N, &argc, argv);
   }