Everything is dollars

There's a great trick I used to use when doing unit conversions using Google's calculator. It's great for asking natural questions in units it knows about, like how long it would take to download 1 gigabyte on dialup or how many years before the Opera House is underwater. But sometimes you have an important question where you want to refer to a unit it doesn't know about, like how many sneezes it takes to fill the Goodyear Blimp.

It turns out the answer is 4.78 million dollars or, uh, 4.78 million sneezes. Dollars make a great "generic standin" unit. They're readily available, easy to remember, and don't accidentally cancel with any other units leaving you with some funny number in megahertz per square nanofarthing or something. Unfortunately, at some point Google added the "unit" unit, which works even better but doesn't feel as clever.

But something occured to me along the way: the dollar really is the perfect everyunit. There isn't a good way to convert, say, degrees celsius into metres, or seconds into kilograms. But there are tonnes of great ways to convert degrees, metres and seconds into dollars. I've sometimes run into the issue of explaining or justifying decisions to people who have decisionmaking oversight but very little knowledge of the decision domain. Or, to put it in another way, they have to check my numbers but they don't know the units.

Maybe you start off explaining that bigger monitors make programmers more productive, or that you need to buy better servers to keep the site up. But as soon as you start talking quantities you immediately run into lots of domain-specific units. How big are these monitors? How much more productive? What's the productivity per inch? You want me to pay x dollars for y servers with z IOPS? What's an IOPS again?

The dirty secret is that you can save yourself a lot of trouble if you can convert everything into dollars and cancel out the units. Figure out dollars profit per IOPS, multiply through by IOPS per dollar cost. You end up with the wonderfully unitless dollars per dollar, which is very easy to reason about.

Everything is dollars. All praise the everyunit.