Matsayi na "anchor" wanda ke bayyana grid na rarrabuwa na MK don taurari masu mahimmanci na O-type, watau waɗannan ka'idojin da ba su canza ba tun farkon karni na 20, sune 15 Monocerotis (O7 V) da 10 Lacertae (O9 V). The Morgan<unk>Keenan<unk>Kellerman (MKK) "Yerkes" atlas daga 1943 ya lissafa ka'idojin O-type tsakanin O5 da O9, amma kawai ya raba haske ga azuzuwan O9s. Ka'idoji biyu na MKK O9 V sune Iota Orionis da 10 Lacertae. Ka'idodin Yerkes da aka sake dubawa ("MK") da aka gabatar a Johnson & Morgan (1953) ba su canza canje-canje ga O5 zuwa O8 ba, kuma sun lissafa 5 O9 VHD (HD 46202, 5226, 5768, 14 HD, 10 Lacertae) da kuma 3 O9 V5 (ma'aunin 348, O9 V). Wannan bita ya sake komawa ga mahimman ka'idoji na MK O9 V da O9 O9 da kuma 10 O9 V.
MKK O9 V