Peek tangent in Unity

Unity use cross(v.Normal,v.tangent)*v.tanget.w
to find biNormal

I guess v.tanget.w=-1 in general situation
and v.tangetw=1 in mirror situation

then I try some test

in 3dsmax (general situation)

in  Unity  w of tangent is  -1

Normal Direction :  red  ball to green ball   

Tangent Direction : red  ball to blue ball   

in 3dsmax (mirror situation)

in  Unity  w of tangent is  1

PS:

set  Absolute  Mode  to  see the UV  coordinate

uv-coordinate-systems-3ds-max-unity-unreal-engine