Originally posted by tuco That is the fundamental units of weight and a far cry from just kilograms.

Perhaps someone can explain why metric countries don't use the modern SI metric system when it comes to weight but use the modern system for all the other units.

Because for all intents and purposes, for all objects of a negligible fraction of the Earth's mass (~6,000,000,000,000,000,000,000,000 kg), weight is directly proportional to mass, in that a 2kg object will have double the weight of a 1kg object. The distinction between newtons and kilograms is insignificant for non-engineering applications near the surface of the Earth. For everyday people, it adds a completely unnecessary step to calculations with units for which there is otherwise a straightforward equivalence.

Or do you also wonder about why people measure some things like sugar or salt in terms of volume, instead of mass, when its involvement in a recipe has nothing to do with volume (e.g. adding a cup of sugar to a pot of water has nothing to do with adding a cup of volume to it)?

As a side note, the mass of an object is impossible to empircally measure directly (unless you can count individual atoms). It can only be determined indirectly through the application of an external force, such as gravity.