The Digital Fibrograph method to estimate fiber maturity was converted for the new model 430, by direct studies of both models, without establishing correlations with data of other instruments based on different principles. Comparative studies were made on the functions L = f(p), L2/p = f(L), M% = f(IM) and the relations n = p0 / p and k = (IM230_A)/IM430 were estimated, where L is the amount reading, p0, the weight of fiber of both combs of Model 230-A, p, the weight of fiber of the comb of model 430, IM, the maturity index and M%%, the maturity expressed in percentage of mature fibers. The final equation obtained for model 430 was: log M% = 2.4123 _ 1,37016 . IM430 with IM430 = L2/p - 0.04857 . L + 0.3616 Evaluation of "F" values obtained by analysing regional variety tests, using both methods and also the equation proposed by Worley Jr. showed the above presented expression to be the most sensible in discriminating among varieties, as for maturity.