Passage: The "anchor" standards which define the MK classification grid for O-type main-sequence stars, i.e. those standards which have not changed since the early 20th century, are 15 Monocerotis (O7 V) and 10 Lacertae (O9 V).The Morgan–Keenan–Kellerman (MKK) "Yerkes" atlas from 1943 listed O-type standards between O5 and O9, but only split luminosity classes for the O9s.  The two MKK O9 V standards were Iota Orionis and 10 Lacertae.  The revised Yerkes standards ("MK") presented listed in Johnson & Morgan (1953) presented no changes to the O5 to O8 types, and listed 5 O9 V standards (HD 46202, HD 52266, HD 57682, 14 Cephei, 10 Lacertae) and 3 O9.5 V standards (HD 34078, Sigma Orionis, Zeta Ophiuchi).  An important review on spectral classification by Morgan & Keenan (1973) listed "revised MK" standards for O4 to O7, but again no splitting of standards by luminosity classes.  This review also listed main-sequence "dagger standards" of O9 V for 10 Lacertae and O9.5 V for Sigma Orionis.

Question: For what was the Iota Orionis and 10 Lacartae standards used for?
MKK O9 V