Using a plus sign in front of a number shows that it is a positive number, as opposed to a negative number, which has a minus sign in front of it.
However, I have seen the expression “+250 BOPD” being used to mean “more than 250 barrels of oil per day,” which is not correct usage. If you want to use a symbol to express “more than,” you should use the greater than sign, >.
Conversely, producing -250 BOPD does not mean “producing less than 250 BOPD;” it means the well is sucking 250 barrels of oil into it from the surface, which is probably not really happening. To express the concept of “less than,” you should use the symbol <.
I've also seen +/- 250 BOPD used to express the idea of "250 BOPD, more or less". For one thing, you should use the symbol ± instead of +/-, but only to express the magnitude of the error bar after a mean or median value.
250 ± 10 BOPD
If you want to use a symbol to express "approximately," then you should use a tilde (~), and it should be right up against the number with no space between it and the number.
But don't overuse the tilde. Engineers like to estimate everything without giving a hard and firm number, but putting a tilde in front of every number in a paragraph can be excessive. You can express the wiggle room in numbers using words like:
• In the neighborhood of
• On the order of
Of these, "approximately" is generally preferred.
To avoid using such a long word too many times, though, you can use other expressions in the sentence that have the concept of approximation already built in, such as:
• Forecasted (not 4cst)
There are plenty of ways, using symbols and verbiage, to cover your options.
Profound Quote of the Day:
“Nobody wants a prediction that the future will be more or less like the present, even if that is, statistically speaking, an excellent prediction.”
– Nathan Myhrvold, American businessman, former Chief Technology Officer at Microsoft, b. 1959