10.00 and 39.99

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These numbers are displayed in a popular photo on the internet these days. They are shown on a gas pump with 10.00 being the gallons of gas bought and 39.99 being the cost, presumably, then, with the cost per gallon of $3.99 and that pesky 9/10 cents.

The title of the photo is something like, “Tough OCD Decision.” But, for the engineer, this decision is simply based on one thing. What are you going to do with the data? If the engineer wishes to calculate gas mileage, keep it at 10.00 gallons. If the engineer is keeping track of costs and budgets, bump it up to $40.00.

Of course, for the engineer, it really doesn’t matter, because once any of these numbers is entered into a spreadsheet that calculates mpg or tracks spending, whether it is a round number or not matters not.

So, to sum up. Engineers enjoy a round number like the rest of the world, though not needing them like some who are insistent upon them, because, engineers have calculators and computers and spreadsheets and algorithms and apps and programs and…. well, you get the idea.

30 or something like it

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30 is an important number for this engineer and every other engineer licensed in this state. It is the number of hours of continuing education each of us must take every two years, or, as they like to say, every biennium (which is two years), in order to retain one’s license.

Every licensed engineer knows this number for their state. Without it we could not don the title P.E., which comes with all kinds of rights and privileges granted thereof.

As numbers go, it is somewhat important, if only to make sure we are able to sign plans and attest that, yes, we’re pretty sure this thing won’t fall down.

26.2

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Another number that screams “Go Metric!” is 26.2. Yes, this is the distance in miles of a marathon. Stickers with only this number on them seem to have proliferated on the backs of cars lately. I am guessing that the drivers of these cars have either driven a marathon course, or watched a marathon on TV.

What is interesting about the 26.2 is that is is rounded off number. The exact number is 26 miles, 385 yards. This is 26.21875 miles, which technically should be on those stickers. But, while one may think that this odd number is because it is a conversion from metric, it is not. The metric distance is 42.195 kilometers.

So, why is the distance of a marathon not an even number in either measurement system? It has to do with some strange story in history which I will not relate here. But I will say that this demonstrates clearly the need for a sensible standard measurement system. No, not the English system. The metric system.

0.0010342%

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This week, we take a look at the engineer and entertainment. Today’s post is about the number 0.0010342%. This represents the percent of movies in which an engineer plays a major role. Notice that this is a percent and it means that in a little more than one out of 10,000 movies, an engineer is given significant billing. Not top billing, of course. That percent is much, much lower. But, there you have it. Engineers provide Hollywood with electricity, clean water, wastewater disposal, engines, sound expertise, computer wizardry, and the list goes on. What does Hollywood give to the engineer in return? A few lines in every 10,000 movies. And most of the movies with engineers are science fiction, so the engineer is usually “out there” socially.

I guess it could be worse. At least not too many engineers are the bad guys.

12

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12 represents a fascinating number for engineers, particularly ones whose efforts provide electricity to our homes.

The average price of one kilowatt-hour (kWh) of electricity is 12 cents. Think about that. One can turn on a 100-watt light bulb and leave it on all day, for 10 hours, and it costs 12 cents. And with CFLs and LEDs, this cost will go way down. The engineer’s wife could dry her hair with a a 1000-watt hair dryer for an hour – if her hair is really wet – and it would cost 12 cents.

I realize that there are many factors that go into the cost of electricity and I certainly do not want to get involved in debates over subsidies, energy sources, environmental impacts, etc. (at least not now). What I wish to do is marvel at a system of creating and distributing electricity that engineers designed and built that contribute greatly to the ability for us to buy one kWh of electricity for 12 cents.

I am sure I don’t have to repeat it here, but engineers are amazing.

365.2422

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Since the new year will soon be upon us, this number is a good one for the engineer. It is the estimation (because it is difficult to measure absolutely precisely), the number of days in a year. Sure, we can be more precise, but for calendar calculations, down to the 10,000th of a day is precise enough for roughing out engineering calculations that will involve longer time frames, such as the cost per year of operating a waste-water treatment facility.

Note that the fraction is why we have leap year every four years. It is almost 1/4 of a day, so adding the day every four years keeps us close to the same start and end of the year, rather than having the seasons shift months if we didn’t have leap years. Of course, we haven’t even begun to discuss the slowing of the earth’s rotation over time. Maybe we will save that for a later post.

Engineers like precision. Instead of a year being 365 days, or even 365 1/4 days, think about a more precise 365.2422 days.

72

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As engineer, I have been trained in many things that some consider not so engineer-ish, but actually are. Economics is one of these. Needless to say, engineers care very much about economics. Frugality is our middle name, or at least one of them. Today’s number comes from economics, and engineers learned of it in a course called something like “Engineering Economics.”

72 is a great number to use for quick calculations, and since engineers are always tending to run numbers in their heads, then 72 is a good number for the engineer. The rule of 72 simply states that for percents of compounding interest, divide the interest rate into 72 and you will roughly get the number of years it takes to double the number (e.g. money invested). So, at 8% interest, $100 would turn into $200 in 72/8 = 9 years.

This is just an estimation and if one uses an interest rate that is very low or very high, then the accuracy of the estimation is, in engineering language, “not as good”. But for quick calculations, 72 works fine. Some may say there is a rule of 70 or 69, and they may yield better results at certain interest rate ranges, but these are estimations, people. Just use 72. It has a lot of numbers that divide into it evenly, and gives fairly close results, for estimations.

72 is a number that has power for the engineer because it 1) is good for running numbers in your head, 2) deals with money, 3) is divisible by a number of numbers, and 4) is just plain useful.

Now, I just have to find an investment that pays 8%, with no risk.

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