Why do my weighing scales have ml and g? My electric weighing scales allow me to set the weighing unit to various different units.  2 of the units are g (grams) and ml (milliliters).  However, considering 1ml at sea level should weigh 1g (and this is borne out in the scales' value; 100ml of water also weighs 100g), is there any particular reason these 2 units of measurement are separate rather than a combined "g/ml" measure?
Well as a chemist the densities of water and any watery liquid like milk will be very close to 1 gram per milliliter (g/ml) -- within a few percent. However corn oil would be off since it is about 0.90 g/ml. Lard seems to be about 0.87 g/ml. So be careful, but I'd guess that most ingredients in a recipe would work if within 10%.