How is mass measured?

When we say an elephant weighs more than a cheetah, we are comparing the gravitational forces acting on them. The weighing scale is simply an instrument that allows us to measure and compare the gravitational forces acting on them. So why do are weighing scales measure in kilograms not in newtons? and are our common weighing scales wrong?

 Common weighing instruments like the electronic balance or spring Balance and bathroom scales actually measure the weight of an object, not its mass these machines, however, are calibrated to give readings in grams or kilograms.


 Using these instruments, an object will have different mass readings at different gravitational field strengths. For example an astronaut steps are a bathroom scale on the moon, the reading will be lower than the reading taken on earth. 

This is the because the gravitational field strength of the Moon is less than that on earth. This means that the weighing scale calibrated for us on earth can not be used on the moon the weighing scale has to be calibrated to the moon's gravitational field strength in order to give accurate mass measurements on the moon. 

 To avoid having to caliarate weighing scales for different gravitational field strength the mass of an object can be measured using a beam balance. 

 A beam balance compresses the gravitational force acting on an object with that acting on standard masses. As both the object and the standard masses experience the same gravitational field strength the mass reading taken from a given object weather on earth or on the moon will be the same.