Methods and apparatus to monitor conditioning machines are disclosed herein. An example system includes a plurality of work rolls to process a continuous strip of material positioned between an entry and an exit of an apparatus. A sensor is positioned downstream from the exit of the apparatus. The sensor measures a first distance between an upper surface of the strip material and a predetermined reference. The sensor measures a second distance between the upper surface of the strip material and the predetermined reference. The first and second distances is measured at at least one of two different locations or two different instances in time as the strip material exits the apparatus. A controller compares the first distance and the second distance to detect material curvature or longbow in the strip material.