The book contains: Main approaches to Errors, different type of errors. Representation of numbers in computer, computer arithmetic, zero in floating point number. Operators - finite differences, average, differential, etc., their inter-relations. Difference of polynomials. Difference equation. Interpolation. Lagrange's methods, error terms. Uniqueness of interpolating polynomial. Newton's fundamental interpolation. Forward, backward and central difference interpolations. Interpolation by iteration.