Archive for August, 2011

Significant Figures and Rounding

August 31, 2011

Engineers are numbers people, and they sure do like to include lots of numbers in their reports. They eat calculus for breakfast. They pepper their writing with equations just to make it look good. Some include lots of decimal places just to make their numbers look more accurate. This is a no-no.

When reporting numbers or when converting from one unit of measure to another, the SPE Metric Standard says “… the number of significant digits retained should be such that accuracy is neither sacrificed nor exaggerated.”

Significant digits, also called significant figures (or Sig Figs, as Mr. Gerlach often referred to them in high school physics class), are defined as those digits that carry meaning about a number’s precision or repeatability. Leading and trailing zeros used as placeholders to establish the order of magnitude do not count as Sig Figs.

Example:
The population of a small town might be 1,200.
The population of a rural county might be 12,000.
The population of a small city might be 120,000.
The population of a big city might be 1,200,000.
In each of these cases, there are two significant figures, the 1 and the 2.

The true precision only allows for two Sig Figs because of births, deaths, people moving in, people moving out, etc. From one day to the next, the third digit would likely vary, so reporting the big city population as 1,204,687 would probably be true for about 30 seconds. And the small town would have to get a new sign made every time a baby was born if it said “Welcome to Krancie, population 1,206.”

Here’s another example:
Say you want to calculate the circumference of a 4-in. pipe with an outer diameter of 4.5 in. You know you multiply the diameter times π, which is 3.141592653…. Would you report the circumference as 14.137166941…? No, that would be too many Sig Figs.

You would have to round the number to the proper number of Sig Figs. How do we do this rounding business?

If the first non-significant digit is a 5 followed by other non-zero digits, round the last significant digit up a number.
Example: 2.8456 rounded to three Sig Figs would be 2.85.

If the first non-significant digit is less than 5, merely truncate at the last Sig Fig.
Example: 2.8446 rounded to three Sig Figs would be 2.84.

But what if it’s exactly halfway? What if the number is 2.8450 and you need to round it to three Sig Figs? Here is the tie-breaker
rule: Round half to even. This is called “banker’s rounding, and is the default rounding method used in IEEE 754.
Examples:
2.8450 would be rounded to 2.84 to make the last Sig Fig even.
2.8550 would be rounded to 2.86 to make the last Sig Fig even.

Now back to our pipe circumference calculation.
Our 4.5-in. diameter pipe has two Sig Figs, and this is the smallest number of Sig Figs in our calculation product. Thus, our answer can only have two Sig Figs. The correct precision for the circumference would be 14 in.

When performing calculations, use as many Sig Figs as are available in the various steps, not rounding in between, but rounding only the final results to the correct number of Sig Figs.

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Units of Measure – Caps, Plurals, Periods

August 25, 2011

It is important to use the correct case, i.e., upper case (capital letters) and lower case (small letters), in your units of measure.

Examples:
G = giga–, whereas g = gram
K = kelvin, whereas k = kilo–
M = mega–, whereas m = milli–
N = newton, whereas n = nano–
T = tera–, whereas t = tonne (metric ton)

When spelling out units of measure, plurals are formed in the usual way.
Examples:  grams, meters, seconds, etc.
Exceptions:  lux, hertz, and Siemens
These are the same in both singular and plural, like deer and sheep.

What about fractions? Values less than one take the singular form.
Examples:  ½ kilogram, 0.75 kilometer

Unit symbols (abbreviations), however, do not take an S at the end to make them plural.
Examples:
1 m, 5 m
1 lb, 2 lb (not lbs, which is a common mistake)

The only situations when a period is used after a unit symbol are:
1) at the end of a sentence   Example: The pipe had a diameter of 36 cm.
2) after the unit abbreviation for inch, so it is not confused with the preposition “in”.
Example: The 36-in. pipe will be delivered next Tuesday.

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Profound Quote of the Day:
“Broadly speaking, the short words are the best, and the old words best of all.”
– Winston Churchill, English statesman, 1874-1965

Under Pressure

August 25, 2011

According to the SPE Metric Standard, the unit of pressure is the pascal, which is defined as one newton per square meter. “Use of the bar is discouraged by the standards organizations,” according to this standard.

One of the excellent recommendations in this document is to distinguish between absolute pressure (relative to vacuum) and gauge pressure
(relative to atmospheric pressure). This is frequently done when using customary units of pressure, such as psia and psig, but this is not done consistently when using metric units like kilopascals (kPa).

Here are some units of measure that “are to be avoided or abandoned,” according to the SPE Metric Standard:
•       angstrom
•       atmosphere
•       calorie
•       candle
•       dyne
•       gauss
•       horsepower
•       mho
•       micron
•       mm Hg
•       stokes

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Profound Quote of the Day:
“Words differently arranged have a different meaning, and meanings differently arranged have different effects.”
– Blaise Pascal, French philosopher and scientist, 1623-1662

Metric Style Guide

August 23, 2011

In addition to the SPE Style Guide, which everybody should have on their desk or hard drive to consult frequently as their technical writing bible, SPE also publishes a Metric Standard to help you report numbers and their units correctly. Here’s the link:
http://www.spe.org/authors/docs/metric_standard.pdf

There is some very interesting stuff in there.
Example:
Did you know that the unit “degree centigrade” is now obsolete?
Yup, it is. So is the planet Pluto. What is this world coming to?
We are now supposed to use “degree Celsius.”

Here are a few other tidbits you will need to keep in mind when writing reports and such:
•       Units of measure are not capitalized unless they are the first word of a sentence or appear in a title.
•       Short forms of metric units are called “unit symbols,” and these are not capitalized unless the unit is named for a person.
•       One exception to this rule in the US is the symbol L for liter.

Examples:
Unit Name       Unit Symbol
meter                 m
gram                  g
liter                    L
newton              N
pascal                Pa

Unit symbols should not be in italics, as italics are reserved for quantity symbols.
Examples:
m       mass
L       length

Fair vs. Fare

August 19, 2011

I was reading (not editing) a news story about integrated oil  companies like Marathon and ConocoPhillips splitting their upstream and downstream business units into two separate companies. The author, a professional writer from Platts, was describing how high oil prices might be favorable for the upstream company, and then I came to a screeching, gasping
halt over the following typo:

“But how would standalone companies fair if prices now started to fall?”

The word “fair” is rarely used as a verb,  and then only when talking about the weather clearing up or two pieces of  something being joined together so the whole is nice and smooth.

Fair is usually used as:
–  An adjective that means pretty, sunny, or impartial.
Examples:
Pray, tell me, who is that fair maiden?
The weather has been the same for months: fair and hot and dry.
That’s not fair! You gave him the bigger half!

–  A noun that refers to a festive or competitive event.
Examples:
The line of people for the job fair snaked out the door in spite of the heat.
Big Tex is a statue of a cowboy that towers over the State Fair of Texas.

The word “fare” comes from an old Scottish word that means “to journey.”
As a noun, fare means food and drink, or the price paid for travel by bus, cab, train, or air.
As a verb, it means to travel or get along. To wish someone “farewell” is to wish them a pleasant journey.

Examples:
The service at that restaurant is superb, but the fare is only mediocre.
I would have taken a cab, but I had no cash for the fare.
How did you fare during your midyear review with Supervisor X?

So back to our typo; the corrected version should read:
But how would standalone companies fare (get along) if prices now started to fall?
Looks like we might be seeing how fairly soon.

Commas, Semicolons, and Parentheses

August 18, 2011

I got a question from the Peanut Gallery today. Barbara asks:
“Where do commas go, inside or outside parentheses? (I always put them inside,) but is that correct?”

Standard Answer: That depends.
Usually, the comma goes outside after the closing parenthesis. The same thing applies with a semicolon or colon.
The exception is when the punctuation is an official part of the stuff inside the parentheses.

Examples:
The routine core analysis data were received this week (see Table 3), and we plan to generate Hall Plots and histograms next week.
The driller originally planned to fish for the lost bottomhole assembly (bit and mud motor); however, the company man decided to proceed with the sidetrack instead.
The following parameters were used (in Petrel): K, Phi, Sw, So, and Sg.

This example has an integrated comma within the parentheses, as well as one outside:
A hardcopy of the Block 78 field development report was sent to the archives (Central Files, which is on the 12th floor), and the electronic version was emailed to upper management and interest partners.

Inversion of Subject and Verb

August 17, 2011

In English, most sentences are constructed by having the subject first, followed by the verb and then rest of the predicate, which can include a direct object and an indirect object, among other things. German, on the other hand, often has the verb at the very end of the sentence, which, when translated literally, can make you sound like Yoda from the movie Star Wars.

Example:
Ich habe sechs Katzen auf dem Gartenzaun gesehen.
I have six cats on the garden fence seen.

Sometimes English sentences require inverting the order so that the verb precedes the subject.
Today let’s discuss some situations where this is done.

1) Questions that start with the verb as the first word.
Example:
Are you going to order that replacement part, or should I?

2) Stating a hypothesis without using the word ‘if.’
Example:
Had I known it was going to rain this hard, I would have brought an umbrella.
In this case, you could also say: If I had known…, which follows the usual order.

3) When a negative or a restrictive phrase begins the sentence.
Examples:
Seldom does she wear a skirt to work, as she often goes out to the field.
Not until next week will the contractor be ready to start commissioning.
Never before had he written such a long report.
Under no circumstances is anyone allowed inside the vessel without proper training.
Rarely does he forget to turn in his timesheet.
Only after marking the orientation on the core should you load the core into the sleeve.

One exception should be noted here:
If “perhaps” is used, then put the subject before the verb in the usual order.
Example:
Perhaps we should reperforate that zone.

4) When the sentence starts with an adjective.
Example:
Brown and crunchy was the grass after 15 straight days of temperatures above 100°F.

5) In exclamations beginning with “how.”
Example:
How industrious was that summer intern!

6) After quoted speech inversion is optional.
Examples:
“We need you to find all the mud logs,” said Dave.
“We need you to find all the mud logs,” Dave said.
When the subject is a pronoun, only invert when writing fiction, not technical articles.
Example:
“Whither thou goest, I shall follow,” said he.
It just sounds more poetic.

Placement of Only

August 17, 2011

Placement of the adverb “only” in a sentence is important because the whole meaning can change if it’s moved to another
location.

Examples:
Only the contractor could install the pump for the $5,000 that was quoted.
(nobody else could do it at that price)
The contractor could only install the pump for the $5,000 that was quoted.
(but not test it or commission it)
The contractor could install only the pump for the $5,000 that was quoted.
(not the accompanying connection lines)
The contractor could install the pump for only the $5,000 that was quoted.
(not the $6,000 that it actually cost)
The contractor could install the pump for the $5,000 that was only quoted.
(but the contract was never signed)

Here’s the Rule of Thumb:
Place the word “only” directly in front of the word to which it applies. In spoken English, this rule is not as important because the sentence stress used by the speaker can eliminate any ambiguity. However, in written English, “only” pertains to or sets a imitation on the word or phrase that immediately follows it, so be careful when deciding where to place it, especially when writing specifications or contracts.

More Examples:
The only data available have come from a laboratory study.
(data were very limited)
The data available have only come from a laboratory study.
(just recently, more expected)
The data available have come from only a laboratory study.
(no field study data like the other fields)

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Quote of the Day:
“Only two things are infinite, the universe and human stupidity, and I’m not sure about the former.”
– Albert Einstein, German physicist, 1879-1955

Ought vs. Aught

August 12, 2011

Here’s another homonym mix-up: Ought vs. Aught

Ought is an auxiliary verb derived from the Scottish word “to owe.” It means “should,” usually
indicating some obligation, advisability, expectation, or moral duty.
Examples:
He ought to finish writing his section of the report before he goes on vacation.
You ought to have a doctor take a look at that sore on your arm.
I really ought to go to the funeral, because we were close friends.

Aught is a pronoun that means “anything” or “all.”
Examples:
Do you know aught about geomechanics? (anything)
For aught I care, you can schedule the meeting on my day off, for I shall not be attending. (all)

Aught is also a noun that means nothing or zero.
Examples:
The gun he used to shoot the deer was a .30-06 (thirty aught six) Springfield.
Her baby was born in ’08 (aught eight).
In fact, in the Nineties (1990s) people were talking about what they would call the next
decade; some suggested calling them the Aughties. Now that we’re in the Tens (or is this decade called the Teens?), what exactly did we decide to call the last decade? Anybody out there in the Peanut Gallery know?

Two other similar words that mean “nothing” are “naught” and “nought.” In British English, nought stands for the numeral zero, whereas naught is a poetic word for nothing. In Yank-speak on this side of the pond, we usually use naught for both, although it is considered old-fashioned.
Examples:
All the effort to drill that troublesome well was for naught; it was a dry hole.
The game tic-tac-toe is called noughts and crosses in England. (fun fact!)

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Typo of the Day:
Exxon Mobile
I didn’t know they were in that business, too –  LOL.
Remember the First Rule of Journalism:
Spell their names correctly

Analysis vs. Analyses

August 12, 2011

There is a whole lot of analyzing going on in the oil and gas industry. If you are doing just one routine core test, you are doing an analysis (singular). If you are doing more than one, you are doing routine core analyses (plural). No, this is not a typo; it’s one of those funky plurals that doesn’t add an –s or –es to the end of the singular word. You certainly wouldn’t say “analysises.”

Another word that makes a plural by changing –sis to –ses is hypothesis. The plural would be hypotheses. Similarly, the singular “thesis” becomes the plural “theses.”

Which brings us to the question:
What is the plural of hippopotamus? Hippopotamuses or hippopotami?
Answers:
“Both,” according to Webster.
“That depends,” according to the engineer. “Depends which one rhymes.”
“Neither,” according to the Grammar Geek. “Use hippos. The readers will know exactly what you mean.”