Alcohol by volume (ABV) numbers on a wine label give the illusion of precision—they go to tenths of percents—but pull back the Alcohol and Tobacco Tax and Trade Bureau (TTB) curtain and, surprise, you discover almost nothing is what it seems.

First, the ABV is a guess rather than a precise measurement. TTB rules permit the number to be off by 1.5 percent in both directions. If the label claims 12.5% ABV, a more accurate presentation would be “somewhere between 11 and 14 percent.”

There are practical reasons for a fudge factor. Wine labels often are designed and printed before the wine is ready for bottling and measurement is possible—and precise measurements often are not possible. Wine is not a singularity. It often comes from various vineyards and ferments in an array of tanks with all the inherent variables. It is possible for bottles of the same wine and vintage to have different ABV levels.

And there are curve balls. If wine falls between seven and 13.9% ABV, it legally can be labeled “white table wine” or “red table wine” with no percentage whatsoever.

Then cometh the specter of tax. Wine that is 14% ABV or less is taxed at $1.07 per gallon, while wine between 14.1% and 21% ABV is taxed at $1.57 per gallon. There can be a pricing incentive for a winemaker to lowball the ABV, but also is a market incentive to go above. As with so many alcohol rules and laws, simplicity and reason are not priorities.

More curve balls: artificially carbonated wine—low-end white wines injected with CO2—are taxed at $3.30 per gallon. Higher quality sparklings made using traditional methods are taxed at $3.40 per gallon.

And we haven’t even ventured into the weeds of tax credits for “smaller” producers—smaller defined as production of 250,000 gallons or less. Credits are ranked in tiers—less produced, higher the credit. And, oh, by the way, credits do not apply to sparkling. No rational person understands the government prejudice against bubbly.

Tasting notes:

• Ruffino Rosé Sparkling Wine NV: Good acidity, crisp red fruits, excellent price point. $12-13 Link to review

• Yamhill Valley Vineyards Estate Grown Rosé of Pinot Noir 2017: Nicely complex pinot noir rosé from quality maker. $16 Link to review

• Duchman Family Winery Montepulciano Oswald Vineyard 2013: Excellent example of Texas montepulciano with assertive black and red fruits. $30 Link to review

Last round: I don’t get it. Why limit “happy” to an hour?