ENGINE ROOM INSIDE THE DEPTHS OF THE SHIP. FOR EXAMPLE

when the bridge personnel wish to change speed they use the handle on the bridge telegraph which in turn moves the pointer in the engine room telegraph to point to the speed desired on its dial. (The pointer on the bridge telegraph, however, remains where it is.) Whenever such a signal is made, a bell also rings in the engine room alerting the engineers that a change is desired. Furthermore, the number of bell rings signifies the speed wanted. For example, three bells can signify full speed astern (backwards). To acknowledge receipt and execution of the order, the engineer moves the handle on his telegraph to match where the engine room pointer is. This moves the pointer on the bridge telegraph dial to correspond with the engine room's telegraph. Thus the bridge can see that the engine room received and executed the order correctly.