If you plan to add other GNAS (ArcheryGB) rounds it might be helpful to get Rules of shooting from http://www.archerygb.org/tools/documents/G0602RulesofShooting-[13846].pdf There is a hell of different target rounds: Imperial (table 3-1), Metric (3-2), FITA (3-3), Indoor (4-1) defined in the doc.
Cheers.