Abstract: A corrugating machine for producing single-faced or double-faced corrugated board which utilizes a thermal sensing system to determine the length of the web in the bridge instead of an ink-based sensing system. The corrugating machine includes means for supplying a first paper web, means for corrugating a second paper web to produce a corrugated paper web, and means for adhering the first paper web to the corrugated paper web to form a single-faced corrugated web. The corrugating machine has a splicer for splicing one of the paper webs at a splice point, means for applying a liquid spot, such as water, to one of the paper webs, and means for thermally detecting the liquid spot after the liquid spot is applied, such as a temperature detector. The corrugating machine determines the length of the single-faced corrugated web based upon when the liquid spot is applied by the applying means and when the liquid spot is thermally detected by the detecting means.