A paper core manufacturer is testing 4 types of paper cores. Three cores of each type are selected and are measured at three positions (either end and the middle) for out-of-roundness at 1 hour, 2 hours, 4 hours, 8 hours, 24 hours and 72 hours post-production. Discuss possible designs and methods of analysis. Discuss analytical approaches if time is treated as (a) a factor or (b) a covariate.