[Aavso-photometry] transformations

[Wm. Mack Julian II]

Since its monsoon time here in New Mexico I've been reading stuff on BVRcIc and how to get my measurments on the standard system. I have BVR filters and just ordered a I based on a message from Arne saying its easier to compute v-i than v-r since there is a greater color difference.

Message to group from Arne from Feb 16 2006

> (B-V) and (V-Ic) are the two color indices that most professionals
> use.
> They have about the same size, and give the most range as a function
> of star temperature.  (V-Rc) is has a much smaller size (about half
> of
> the other two indices), so transformations are less accurate.
> V and Ic have completely separate passbands, so transforming to
> other systems is cleaner.  Ic is less affected by dust and
> atmospheric
> extinction than is Rc.  Ic is easier to measure for red stars.

Bah, hit send before I got to my question. I think I understand that to find transforms you plot:

B-V vs b-v and take 1/m to get Tbv
V-R vs v-r and take 1/m to get Tvr
R-I vs r-i and take 1/m to get Tri
V-R vs V-v and m is Tv
R-I vs R-r and m is Tr

is there a Ti? Would you normally report using a standard mag say V and V-I as color inidice something like B and B-V?