Many tasks in safety-critical embedded systems have hard real-time characteristics. Failure to meet deadlines may result in the loss of life or in large damages. Utmost carefulness and state-of-the-art machinery have to be applied to make sure that all requirements are met. To do so lies in the responsibility of the designer(s). Fortunately, the state of the art in deriving run-time guarantees for real-time systems has progressed so much that tools based on sound methods are commercially available and have proved their usability in industrial practice.