Aitken's criteria for double stars

A couple of months back, Mark G gave it as

log d + 0.2 m 2.8

where d is the separation in arcseconds, log is base 10, and m is the
magnitude of the secondary. For example, if the separation is 10
arcseconds, then the secondary must be no dimmer than magnitude 9 to
satisfy Aitken's criterion, since

log 10 + 0.2*9 = 1 + 1.8 = 2.8


I now understand that Mark was incorrect in what he stated and that it
is the combined magnitude of the pair that represents the value of m!

I have tried twice to contact Mark without luck so I hope he still
reads this newsgroup.