The antidote to impulse buying. Feed it a price and honest usage guesses, and it tells you whether that thing is a bargain, a luxury, or a future eBay listing.
Cost-per-use = price ÷ total uses over the keeping period. Cost-per-hour-of-joy divides again by hours per use and weights by the joy factor, because a £300 guitar you play daily beats a £30 gadget you touch once. All estimates, no judgement — except the tiny bit of judgement at the end.