A Calgary-based company (Piedmont Pipelines) has been awarded a contract to lay a long stretch of pipeline. The planned schedule for the laying of pipe can be considered to be accurately known for the duration of the project (18 months). Because of weather conditions and the availability of labor, the rate of placement of the pipe is not constant throughout the project. The supplier of the pipe offers a discount structure for purchases. Outline an analysis that would assist Piedmont in deciding on the purchase schedule for the piping.