When a grocery manufacturer offers a new size of an existing product, it often appears to be simply another way of increasing the price per ounce. Maybe the new size offers convenience to some consumers, but when the price per ounce goes up along with added convenience, the careful shopper could avoid the new size, to discourage such behavior.

Anyway, when Mr. Tidbit spotted the new Satisfying Selections line of larger offerings in the Weight Watchers Smart Ones line of frozen foods from Heinz (each emblazoned "30% larger serving"), he assumed he knew what was up. The five Satisfying Selections, in microwave-steaming bags instead of microwave trays in boxes, each weigh in at 11.7 ounces, compared with the 9-ounce servings of the many regular Smart Ones items, which is indeed 30 percent more food.

Imagine Mr. Tidbit's shock when he calculated the price per ounce: At least at the store where he found them, the difference was less than half of 1 percent: Regular Smart Ones cost $3.29 (36.55 cents per ounce) and the 30-percent-larger Satisfying Selections cost $4.29 (36.66 cents per ounce)! Holy Toledo!

None of the new products appears to have exactly the same recipe as an existing Smart Ones offering, but even supposing that the new products have cheaper ingredients -- and Mr. Tidbit has no idea whether that's the case -- he feels he needs to nod to Heinz and Weight Watchers for at least appearing to hold the line on prices.

And a bad one The other common price-increase mechanism is to keep the shelf price the same but shrink the package -- or the contents of the package. An angry reader alerted Mr. Tidbit to a perfect example: Quaker granola bars, until recently 10 (0.84-ounce) bars in an 8.4-ounce box, are now eight (0.84-ounce) bars in a 6.72-ounce box, at the same shelf price -- a surprising 25-percent price-per-ounce increase. Similarly, the chocolate-covered Quaker Dipps granola bars have gone from eight bars per box to six -- a 33-percent price-per-ounce increase!