A film thickness measuring method and apparatus capable of measuring a film thickness with high accuracy even if the spectral reflection intensity is not sufficiently high to measure an accurate film thickness and gives a poor SN ratio. The regulator value is monitored for the attainment of a first predefined threshold value, and when the latter is reached, a lambda quality value is determined which is representative of the deviation of the measured cylinder-specific airfuel ratios assigned to the respective cylinders. The first terminal of the printer can be configured to communicate via a first plurality of electrical contacts using a USB protocol and via a second plurality of electrical contacts using another protocol. It is determined whether masking is set for each of the layout-adjusted containers.