Here we have presented 3, 4, and 5 points explicit finite difference 
formulae along with the error terms, for approximating the first and higher order 
derivatives for unequally spaced data. By differentiating the equation (1), finite 
difference formulae for higher order derivatives can also be obtained. These 
formulae can be used directly to solve the ordinary and partial differential 
equations and will serve to approximate the derivatives at the unequally spaced 
grid points. A scientific program of the above formulae will facilitate the use of 
any finite difference formulae of desired derivatives.