text: how can we calculate precesion formula?   depends on what is precessing!    could you mean a foucault pendulum? http://www.phys.unsw.edu.au/~jw/pendulumdetails.html  the axis of a gyroscope? http://www.frc.ri.cmu.edu/~alonzo/course/pos_se~1.fm5.pdf  an electron's orbital spin? http://www.mathpages.com/rr/s2-11/2-11.htm  mercury's perihelion? http://psroc.phys.ntu.edu.tw/cjp/v8/24.pdf  they all have different derivations!