text: depends on what is precessing!  \n\ncould you mean a foucault pendulum?\nhttp://www.phys.unsw.edu.au/~jw/pendulumdetails.html\n\nthe axis of a gyroscope?\nhttp://www.frc.ri.cmu.edu/~alonzo/course/pos_se~1.fm5.pdf\n\nan electron's orbital spin?\nhttp://www.mathpages.com/rr/s2-11/2-11.htm\n\nmercury's perihelion?\nhttp://psroc.phys.ntu.edu.tw/cjp/v8/24.pdf\n\nthey all have different derivations!