Many year ago, I worked on a project providing training simulations for the Reactor Shutdown Safety Sequencing Equipment (RSSE) of a UK AGR power station - the project manager had been involved in the construction of the plant and explained that the equipment involved actually used mechanical sequencing essentially based on clockwork as it was designed using technology that was really trusted when the AGR plants were first designed in the 1960s - which basically meant 1940s level technology.

Edit: Pretty sure I have the words in RSSSE correct though perhaps not in the right order.