## The Tilde vs. +/-

There are a whole lot of approximations made in the oil and
gas business, and expressing them correctly is important.

Sometimes the tilde ( ~ ) is used to indicate an approximation.
Example:  ~25 means “approximately 25”
Note that there is no space between the tilde and the number following it.

There are two ways to make a tilde on the computer.
On my keyboard there is a key to the left of the numeral 1 (above the Tab key) that has the tilde as the Shift character. The other way is to Insert a Symbol in Word, with ~ being the Unicode 007E symbol.

There are two ways to make a tilde by hand. You can go up before you go down when making the wave (this is the correct way), or you can go down before you go up. The Nike Swoosh logo goes down and then up, but it doesn’t come back down again.
(My personal favorite use of the tilde is over the n in jalapeño.)

I have seen engineers use +/- (pronounced “plus or minus”) instead of the tilde when expressing an approximation.
We plan to drill +/-34 wells in the field by 2019.

This is not correct for two reasons:
1)  Rather than using a plus sign, a slash, and a hyphen, one should Insert the Symbol ±, which is Unicode 0081.
2)  The ± symbol is used to indicate the precision of an approximation, the confidence interval, the standard deviation, or the error in a measurement.

Good Examples:
We plan to drill 34 ±2 wells in the field by 2019.
That gauge goes up to 15,000 psig with an accuracy of ±0.1% full scale.
Note that there is no space between ± and the number following it.

Now, revisiting our Bad Example, that sentence would mean that there is a difference of 68 wells between the lowest number of wells you plan to drill and the highest number of wells you plan to drill in that field by 2019. I don’t think the bosses would go for that kind of uncertainty.

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Fun Fact of the Day:
The tilde is used in mathematics to denote equivalence.
x ~ y means that “x is equivalent to y”
Sometimes the math tilde is called a “twiddle.”
So x ~ y is read aloud as “x twiddles y.”
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Another Fun Fact of the Day:
The symbols ± and ∓ are used in chess notation to denote an advantage for white and black, respectively.