Wow! Fascinating and useful discussion. Glad you raised the question, Liza. Not a silly one at all.
If I understand Jeanne correctly, the ml/fl oz setting on such scales merely switches from saying, for example, 1 lb. with the dry weights function to 16 oz. when using the fluid weights function. In metric, the same example would be 454 grams to 500 ml. Being able to switch back and forth like that would be useful in some circumstances as Jeanne describes. It’s hard to calculate in your head if you need 0.875 of a pound! And not everybody bakes often enough to know right off the top of their heads that 1.5 lb is 1 lb. 8 oz is 24 ounces is 681 grams, is 0.681 kg etc.
I think the main source of confusion here is how the scale seems to say that you can use the ML/FLOZ setting for recipes that are given in volume. Not true. With either button, you’re working in weights. Liquids can be weighed just as easily as dry ingredients. Recipes written in volume (cups and teaspoons) that call for, say 250 ML/8 oz are actually asking you to use a measuring cup. If the ingredient were honey, for instance, they would want you to go by the lines on your measuring cup but, by weight, you’d need 11.75 ounces. The only reason I know that is from Rose’s chart that I mentioned in the earlier post. You’d be short by 3.75 ounces, if you weighed out 8 fl ounces on your scale.
Different ingredients vary tremendously in what they weigh per cup. My example above is honey, which is way heavier than water. They’re both liquids. Measure out one cup of each and you’ve got, according to the volume measures on the side of your cup, 8 fl. oz or 250 ml in each cup. Put them on your scale, however, and you see the figures I gave above for honey (11.75oz/336 g) while the water weighs just over 8 ounces and 236 grams. That’s one of the reasons weights (dry or liquid) are so much more accurate than volume. But I wouldn’t be afraid of the ml/fl oz button on your scale. It’s useful in the way described.
Work with it for awhile. It will all become clear. Again, thanks for raising the question. I had no idea there were scales that weighed in ml/fl oz. Good to know.