A division of a company manufactures two products, which are in high demand in the defence industry Product A is stamped out in a machine press, at the rate of 10,000 per hour. Product B is identical to product A, with the exception that it is made from thicker steel, and requires the machine press to be recalibrated. Product A is produced on the day shift and product B is produced on the afternoon shift, allowing set up changes to be done between shifts. In this case, set up hours are related to which of the following? labour hours units of output machine hours batches of output the number of customers