The cheapest thing in the room

A school was deciding between two projectors. One cost four million dong, the other seven. The cheaper one was chosen, which is how most such decisions go and is frequently the wrong answer for a reason that has nothing to do with quality.

The purchase price of equipment used daily for years is usually a small part of what it costs. The larger part is running cost and attention. The cheaper projector used a lamp costing eight hundred thousand dong that lasted about a year. The other used one lasting four. Over five years the lamps alone reversed the comparison.

There is a second cost that nobody budgets. The cheaper projector took forty seconds to warm up and occasionally needed restarting. Forty seconds, five times a day, across two hundred school days, is about eleven hours of a teacher and thirty students waiting, every year. Nobody records this anywhere and it is by a wide margin the largest number in the comparison.

The general version is worth carrying around. When something will be used repeatedly by several people, the purchase price is a number that appears once and the time cost appears thousands of times. Multiplying before deciding takes two minutes.

This is not an argument for always buying the expensive option. It is an argument for comparing the right quantity, which is total cost over the life of the thing, including the part measured in other people's minutes.