A method of providing a set of alignment marks on a substrate including the following steps. The system comprises distance determining means configured to determine, using electromagnetic radiation signal reception means, at least a distance between the system and an aircraft. In one example, the method arranges the work units into a directed acyclic graph representing execution priorities between the work units. The first connecting component has a second connecting device, which interacts with the first connecting device in such a way that the first connecting component is detachably connected to the receiving sleeve. In one example, the method may include authenticating a user via a first method utilizing input received from the user, authenticating the user via a second method utilizing a device associated with the user, and authenticating the user via a third method utilizing a security token. R3 groups and R4 groups are each independently hydrogen or C1-6 alkyl andor the two R3 groups andor the two R4 groups together form a C3-6 spiroalkyl group, provided that at least one R3 or R4 group is not hydrogen; and X is selected from hydrogen, halogen, cyano, alkyl and alkoxy.