I bought a medium sized above ground pool that the kids rarely used. More work than it was worth.

Next I bought a nice trampoline for the kids and the second it showed up at my door my dad commented that he thinks it was a waste of my money and that the kids don't even use the pool and the same would be true for the trampoline.

Well he has since apologized many times over after realizing my kids would put about 6 hours a day on the thing in the summer and even on some of the less then optimal weather days put in some time. My dad now keeps talking about the cost per hour the trampoline has gotten ($500 trampoline - 500 hours use = 1$/hr), well now I think he calculates it by the cents per hour no longer dollars.