That is nonsense. 500 g are 500 g. In SI units. Or 0.5 kg.

Again nonsense and **not related to either SI or imperial units.**

1 M is the prefix for Mega which means 10^6.

So 1 Mg = 1000 kg = 1 000 000 g

Just because 1 kg is the base unit doesn't mean that the prefixes like k, M, m etc. lose or change their meaning. 1 kg = 1000 g because k ist the prefix for kilo meaning 1000.

Absolutely correct. So, when using SI units, the user obeys the SI convention and enters 1000 kg as 1000, and derives their result, never looking back, and looses 3 decimal places. Now if the original formula reads U = mgh and explicitly and in no uncertain terms states that m is to be expressed in kg, not to meet calculation convention, but rather to meet physical criteria, then I am at error, and yes Virginia, a Mg mass can be raised 3 m ( under the influence of Earth's gravity ) with the energy stored in 3 AA cells. So my question is currently, " In the explanation of the formula U = mgh, when the explainer states that mass is to be in kilograms, is that conversion made to satisfy a method of math or is it to adjust things to qualify the value into the real physical world?" Personally, I think that m was meant to be in grams, and the instructor, say working in the SI system, mentions that 1,000,000 grams is to be expressed in kg, ( 1000 kg ) which is further botched up by the fact that in the SI system assumes that mass is expressed in kg, therefore entering the value as 1000 g, and instructor leaves his explanation at that point. Leaving the student twisting in the wind. I agree that convention needs to be set in order that values can be used worldwide, but I contend that most people do not have a grasp upon the true affect of formula manipulation. So I need to know the exact intent of the formula, U = mgh. Further, if the quip, "expressed in kg," is true in the formula E = mc², I will need to mine a thousand times more uranium for the reactor in my basement !