Weighing scale
The balance (also balance scale, beam balance and laboratory balance) was the first mass measuring instrument invented. In its traditional form, it consists of a pivoted horizontal lever with arms of equal lengththe beamand a weighing pan suspended from each arm (hence the plural name ""scales" for a weighing instrument). The unknown mass is placed in one pan and standard masses are added to the other pan until the beam is as close to equilibrium as possible. In precision balances, a more accurate determination of the mass is given by the position of a sliding mass moved along a graduated scale. Technically, a balance compares weight rather than mass, but, in a given gravitational field (such as Earth's gravity), the weight of an object is proportional to its mass, so the standard masses used with balances are usually labeled in units of mass (e.g. g or kg).
Model aircraft
Scales are not usually random, but are based upon simple divisions of either the Imperial system, or the Metric system.
For example, 1:48 scale is 1/4" to 1-foot (or 1" to 4 feet) and 1:72 is 1" to 6 feet, while metric scales are simpler, such as 1:100th, which equals 1 centimeter to 1 meter.
1:72 scale was first introduced in the Skybirds wood and metal model aircraft kits in 1932. Skybirds was followed closely by Frog which produced 1:72 scale aircraft in 1936 under the "Frog Penguin" name. According to "Fine Scale Modeler" magazine, 1:72 was also popularized by the US War Department during the Second World War when it requested models of single engine aircraft at that scale. The War Department also requested models of multi-engine aircraft at a scale of 1:144. The War Department was hoping to educate Americans in the identification of aircraft. These scales provided the best compromise between size and detail. After WWII, manufacturers continued to favor these scales, however kits are commonly available in 1:48, 1:35, 1:32, and 1:24 scales. The French firm Heller SA is one of the few manufacturer to offer models in the scale of 1:125, while 1:50th and 1:100th are more common in Japan and France which both use Metric. Herpa and others produce promotional models for airlines in scales including 1:200, 1:400, 1:500, 1:600, 1:1000 and more. A few First World War aircraft were offered at 1:28 by Revell, such as the Fokker Dr.I and Sopwith Camel.