[Aavso-photometry] Where can I find info on accurate magnitudes?

[barbharris1]

First, I would like to preface my question with the statement that I am
a beginner.  I took some images of GW Lib in blue filter since the star
was so bright.  The comparison star sequence that was posted on the web
site did not list the 9.4 star that I wanted to use as a comp star (this
was the closest in mag to the variable).  When I went on line to the
SIMBAD astronomical data base site to look up the Tycho magnitude for
this star (TYC 6766-1577-1) it listed a BT mag of  9.736.  Does the T
stand for Tycho and is it ok to use this magnitude for my comp star?
Also, when I looked under recent observations for this star in AAVSO, an
observer from 4/13 (CWT) has the same Tycho star identified but has the
mag as 9.706.  Is there someplace where there is other magnitudes for
Tycho stars listed or is this a typo by him?  Is this the most accurate
place to get the magnitude info if AAVSO does not have the magnitude
info?
 

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