Typically there are two alternatives in a replacement analysis. One alternative is to replace the defender now. The other alternative is which one of the following?

(a) Keep the defender for its remaining useful life.

(b) Keep the defender for another year and then reexamine the situation.

(c) Keep the defender until there is an improved challenger that is better than the present challenger.

(d) The answer to this question depends on the data available for the defender and challenger as well as the assumptions made regarding the period of needed service and future challengers.