>>But if one is expressed per kilo and the other per 100g, the prices will even look the same, just the decimal point will shift one place.
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>People know that some product is always in pounds and another in ounces. They will feel lost looking at grams, or will demand the guy (head) who can divide by 28.

It is not always in pounds. Next time I'll take the camera to the grocery. The house brand is in ounces, the brand brand is in pounds - same product.

And that's in a grocery which prides itself with having the prices also recalculated into per unit prices, so one product being in 7oz bottles can be compared to the other which is in 10oz bottles. But they don't recalculate all the instances of the same product into same units, probably to promote the house brand.