This work evaluates the impact of augmented reality (AR) technology to support operators during manual industrial tasks. The work focuses specifically on monitor-based augmented reality as a solution to provide instructions to the operator. Instructions are superimposed directly onto a video representation of the physical workspace and are displayed on a standard monitor. In contrast to previous AR solutions proposed to support manual tasks, the current work is more industrially acceptable because it meets most of the industrial requirements and it is cost effective for a deployment in an industrial environment. The developed prototype is described and evaluated by means of a user study to compare the monitor-based augmented reality solution to provide instructions and the traditional method. The test shows that AR can be a valid substitute to support the operators during manual tasks because it allows them to be more time efficient and it reduces their mental workload compared to traditional instructional manuals.