Sometimes it is necessary to begin a survey starting at the end of a branch passage. When this happens, the shots in the branch have no connection to the rest of the survey until the shots reach the main survey. This kind of shot is called a "hanging" shot. B1 and B2 in the diagram are hanging shots.
How The Compiler Processes Hanging shots. In a hanging shot, neither station is defined. As a result, the computer cannot process the shot when it reads it. It has to wait until one of the stations has been defined. It does this by suspending the processing of the shot until later. This is called a suspended shot. The program puts suspended shots into a list, which is reprocessed periodically to see if the parent stations have been defined yet.