"Mixing of $^1P_1$ and $^3P_1$ for the heavy-light mesons in HQET"

There are two conventions for the mixing between the heavy-light mesons $^1P_1$ and $^3P_1$. I clarify the origin of the difference between two and suggest which is the natural results of heavy quark effective theory in the potential model. This affects the analyses so far done by many people.