One great way to make sure you’re getting the best deal when shopping is to compare unit prices you typically find on store shelves - the price of a product by ounce, pound, quart, or other unit of measure.

But that’s only if the unit prices are accurate.

In September 2006, Consumer Reports Money Adviser reported finding a New York-area Target and A&P supermarket using different units of measure to unit-price various brands of the same product, making price comparisons difficult. For instance, the A&P displayed prices of spaghetti sauce in units of ounces, pounds, quarts and millileters, depending on the jar.

Now the Connecticut Department of Consumer Protection has accused Target of posting incorrect unit prices during separate visits by a state inspector to the very same store. 

During a September inspection of the Stamford, Conn., Target, the state said it found that 17 of 50 products were incorrectly unit-priced, more than during a visit to the same store in July. That was the result even though the store had been warned about the problem during the earlier inspection, the state said. A hearing for the chain, which could face civil penalties, is scheduled for October 27.

Given these unit price inaccuracies and failure of at least some retailers to correct them even when they’re alerted, our advice is to bring a calculator when you’re shopping and verify the prices yourself. Otherwise, that jug of Tide that you thought cost less per ounce than that bottle of Cheer, might actually have cost you more.

By the way, don’t assume that the larger container of the same product is a better value, even if your comparing just one brand. Some items, such as tuna fish and ketchup, often have a so-called “quantity surcharge.” In other words, the large container costs more per unit than the smaller one..–Anthony Giorgianni