Abstract: A programmably alterable incrementing system particularly adapted for use in conjunction with an apparatus for selectively indexing punch cards or like sheet material through a work station; such apparatus being particularly susceptible to errors in tolerance such as may be due to inaccuracies in mechanical components, but which are particularly attributable to variation in humidity conditions. Means including a stepping switch are provided to introduce a corrective factor, as needed, into the indexing system to ensure that the required correspondence exists between the actual and the intended increment imparted to a punch card as it is advanced through the work station.