Inspect or monitor?

Much is made of condition monitoring or predictive maintenance in modern maintenance practice. It is not always the best way to deal with items which give detectable warnings of failure. The paper presents simple ‘Markov’ models which can be fed into a programmable calculator to compare the costs of continuous monitoring with inspection at optimized mean random intervals. Although the author’s instinct is to keep it simple, some elaborations of the basic model are offered to show its versatility.