Abstract: A crane includes a boom adapted for lifting a load and a sensor adapted for measuring the side deflection or twist of the boom during the lifting of the load. The crane may also include a system for detecting side deflection in the boom using a first sensor mounted to the boom for sensing a first value corresponding to deflection of the boom, a second sensor for sensing a second, reference value, and a controller for comparing the first and second values to determine a deflection amount. An operator may be notified if the side deflection or twist values exceed a predetermined value. Side deflection or twist values for the boom during a lifting operation may also be logged by a data recording device for later use.