AR technology has started replacing classical training procedures and is increasingly adopted in the industrial environment as training tool. The key challenge that has been underestimated is the required effort of authoring AR instructions. This research investigates the context of humanoperated assembly lines in manufacturing factories. The main objective is to identify and implement a way of authoring step-bystep AR instruction procedures, in a manner that satisfies industrial requirements identified in our case study and in the literature. Our proposal focuses in particular on speed, simplicity and flexibility. As a result, the proposed authoring tool makes it possible to author AR instructions in a very short time, does not require technical skills and is easy to operate by untrained workers. Compared to existing solutions, our proposal does not rely on a preparation stage. The entire authoring procedure is performed directly and only inside an AR headset.