Well, living in Chile - and expecting guests to visit from the US - means that there are many things to get accustomed to. Including measuring things differently. Since Chile - like most of the rest of the world - uses the metric system, and the US - like few places in the world - chooses to stick to an arcane system of weights and measures (with its citizenry either blissfully unaware of any different reality or loudly proclaiming anything different to be just plain weird), it is necessary - from time to time - to stop and recognize that visitors don't have the luxury of time to get accustomed to what a particular measured value means. Sure, sure, it's easy to use back-of-the-envelope conversions for simple, everyday things:
"One meter is a little longer than 3 feet."
"One kilogram is a little bigger than 2 pounds."
"One kilometer is a little more than 1/2 mile."
"One hundred kilometers per hour is roughly 60 mph."
"One liter is a little more than 2 pints."
Sure, they're only kind of correct, but it lets visitors from the US get a grasp on the kinds of weights and distances that are discussed, and for the day-to-day kinds of uses, this sort of calculation puts the results in the correct range at least. So when you're buying stuff at the store, you can make a quick conversion from kilograms to pounds; when you're looking at walking distances in the city, you can make a quick conversion from kilometers to miles; etc.
However, less common conversions don't necessarily have such easy rules of thumb. One such is the price of gasoline. If you are going to rent a car in Chile, you're likely going to want to know how much you're paying for gasoline. But while you might know that one liter is roughly 2 pints (and - by extension - there being 8 pints in a gallon, that 4 liters is somewhat more than 1 gallon), combining that knowledge with an exchange rate is not that simple. What would be great is a simple unit conversion.
Well, the exchange rate between the US Dollar (USD) and Chilean Peso (CLP) has been relatively stable at between 540 CLP/1 USD (or 0.001852 USD/CLP) and 565 CLP/1 USD (or 0.00177 USD/CLP). We can use this in the following unit-conversion:
USD/Gallon = x CLP/Liter
USD/Gallon = x CLP/Liter * 0.26417205236 Liters/Gallon * USD/CLP
USD/Gallon = 0.26417205236x CLP/Gallon * USD/CLP
(Using 0.00177 USD/CLP to be conservative:)
USD/Gallon = 0.26417205236x CLP/Gallon * 0.00177 USD/CLP
USD/Gallon = 149.2497x USD/Gallon
x = 0.0067
Or, to give it a nice back-of-the-envelope-calculation value:
"900 Chilean pesos/liter is roughly equivalent to $6/gallon."
And - given that gas prices in Chile are ~830 CLP/Liter (~$5.50/gallon) - this back-of-the-envelope conversion rate is kind of handy. (I did write about Chilean vs. US gasoline prices before; general trends haven't changed too much.) By the way, did you know that the price of gasoline in the US is the lowest among OECD countries and non-petrostates?
Next: Unit conversions of square area.
NOTE: For people familiar with UK pre-metric weights and measures, these numbers may seem to be a little off. Remember that these conversions are for people from the US, where liquid measures are slightly smaller than the those used in the UK pre-metric. In other words, people who refer to the US system of weights and measures as the "imperial system" are technically wrong. (Unless they mean to say that the "imperial" refers to the US empire, and not the British one.)