I always forget which is which and end up checking each time I adjust the gears. The way I check is to bring my head down so my left ear is about level with the rear axle and peek at the back of the derailleur with a torch. Can usually see the end of the screws, then shift to the biggest or smallest ring and see which screw end is closer to the armature. You can push the derailleur that little bit further so the armature meets the screw end while you watch it to be certain.