This idea is solely from Martha. There is only one Martha, and I will not soil her good name by the inclusion of a surname.
"For even wear and a longer life, a mattress should be flipped four times a year (alternating between end-over-end and side-over-side rotation). Hotels keep track by marking each end of a mattress: one says “January” (right side up) and “April” (upside down), the other “October” (right side up) and “July” (upside down). Whenever one of those months rolls around, adjust the mattress so that the appropriate month’s name is right side up at the foot of the bed."
Since this tip was written in a 2003 issue of her magazine, pillow-top mattresses have been introduced, I’m aware. So this little tip obviously won’t apply/work in that case. So what if you do have a pillow-top mattress? Well, you must be doing very well for yourself to afford one of those. Congratulations.