Whether you want to know the mass of produce at the store to determine how much you'll need to pay for it, the mass of materials in a chemistry lab to know how much of each to use in a chemical reaction, or the mass of yourself for health reasons, a tool to meet your needs exists. The structure of different scales varies in accordance with exactly what each type is designed to measure.
A triple-beam balance is handy when you need to measure items with great precision, as in a science lab, where things are often quantified in grams or milligrams. These scales use pendulums rather than springs. They include a measuring pan on which to place whatever you're measuring and have three different movable pieces -- a 100-gram, a 10-gram and a 1-gram slider. You move each of these individually until the object is balanced. Unlike spring scales, these are unaffected by small changes in gravitational force that may occur when you move from one part of the Earth to another.
If you or your parents have an older bathroom scale, it probably has an analog readout; newer ones are almost invariably digital. In either case, such scales are useful for determining your mass to within about half a pound in the case of an analog model, or up to 0.1 pounds for a digital scale. These scales make use of Hooke's law, which states that the distance (x) a spring is stretched is directly proportional to the force (F) applied to it: F = (k)(x), where k is a constant. The spring system within a given scale is calibrated to give a numerical reading corresponding to this force.
If you've driven on U.S. Interstate Highways, you've probably seen signs for weigh stations, which are like rest areas for tractor-trailer trucks. When these are open, truckers must pull over and have their rigs weighed to make sure that they don't exceed the federally imposed limit of 80,000 pounds. The scales used are industrial-caliber platform scales, which function in the same basic way as other scales but typically rely on levers and masses owing to the sheer mass of the objects being weighed.
Scales aren't the only tools used to measure the mass of objects. Using standard astronomy instruments such as telescopes and light analysers, scientists can estimate the masses of entire galaxies. They do this by looking at the orbits of stars in a spiral-shaped galaxy, such as our own Milky Way, around the galaxy's center. Using a mathematical equation relating mass to rotational speed, orbital radius and the universal gravitational constant called G, scientists can calculate the mass of material enclosed within a given radius.