True North determined for the construction of Vastu homes is established by a projection of the earth's axis to an imaginary point within the celestial constellations. The north star is used as the reference point. Read this article and tell me if you conclude that the reference point is not consistent over time.
http://en.wikipedia.org/wiki/North_celestial_pole "The celestial poles do not remain permanently fixed against the background of the stars. Because of a phenomenon known as the precession of the equinoxes, the poles trace out circles on the celestial sphere, with a period of about 25,700 years. The Earth's axis is also subject to other complex motions which cause the celestial poles to shift slightly over cycles of varying lengths; see nutation, polar motion and axial tilt. Finally, over very long periods the positions of the stars themselves change, due to the stars' proper motions."
