by  C. Thorsten

Science teachers like to remind students that they're measuring the mass of objects rather than the weight.   Grams are, after all, a unit of mass, not weight.  Technically, however, "weighing" may be more appropriate depending on the method of measurement.

• When one mass is measured against another on a two-pan balance, the result will be the same whether it's done on the moon or on the earth.  A 1-kg mass will balance a 1-kg mass, no matter where it's measured.  The hanging balance gives a true mass measurement.

• When a mass is measured on a top-loading electronic scale that uses a pressure transducer (nearly all of them do!), the scale would show the object as lighter on the moon than on earth.  A 1-kg mass will read about "167 grams" on the moon, if that kind of scale is used (surprise!  that kind of scale doesn't measure mass!)

Truly, the object has the same mass regardless of where it is.  It's just that a laboratory scale based on a pressure transducer is displaying units of mass but has obtained that information from a weight measurement.

The top-loading scale was intended to be used only on earth, so its design has ensured that a certain force pressing down on it-- in other words a certain weight--  will give a particular "mass" reading.

When someone tells you to "mass" an object, ask what kind of scale it is (you might also point out that "mass" is not a verb).  If it's a top-loading scale with a pressure sensing mechanism, you are technically weighing the object and getting a "mass" reading based on a conversion.  If it's a balance where your object is being compared against other objects of known mass (many of us stubbornly call them "weights", which they also are), you are in fact getting a direct mass reading.

It all becomes of little relevance as long as you know the technical difference between weight and mass.  Mass is a certain amount of matter.  Weight is a downward force exerted by that matter in a gravitational field. 

Here's a secret:  later on, when working in industry or academia, the idea of mass is usually just assumed.  The concept of "massing" an object is impressed on young minds to get them thinking in science terms;  once past that stage, we usually refer simply to "weighing" things in the lab. 

"Listen, do me a favor and weigh out 5.0 gram of Tris base". 

Tradition dies hard.