diff --git a/src/services/trainService.services.js b/src/services/trainService.services.js
index 0520809..ddd55e9 100644
--- a/src/services/trainService.services.js
+++ b/src/services/trainService.services.js
@@ -14,6 +14,8 @@ async function findByHeadcode(headcode) {
     scheduleEndDate: {$gte: now},
     daysRun: {$in: [shortDay]}
   };
+  // At this point, the returned objects need sorting to ensure the correct object is returned.
+  // C, N, O, P is the order - C being the preferred, then N, then O and finally P.
   return db.query('timetable', query);
 }