A scale or balance is a device to measure weight or mass. These are also known as mass scales, weight scales, mass balances, weight balances. 天平是用来测量重量或质量的装置。它们也被称为质量秤、重量秤、质量秤、重量秤。

The traditional scale consists of two plates or bowls suspended at equal distances from a fulcrum. One plate holds an object of unknown mass (or weight), while known masses are added to the other plate until static equilibrium is achieved and the plates level off, which happens when the masses on the two plates are equal. The perfect scale rests at neutral. A spring scale will make use of a spring of known stiffness to determine mass (or weight). Suspending a certain mass will extend the spring by a certain amount depending on the spring's stiffness (or spring constant). The heavier the object, the more the spring stretches, as described in Hooke's law. Other types of scales making use of different physical principles also exist.

传统的天平由两个盘子或碗组成，它们与支点的距离相等。一块板上有一个未知质量（或重量）的物体，而已知质量则加到另一块板上，直到达到静态平衡，两块板趋于平衡，当两块板上的质量相等时就会发生这种情况。... 弹簧秤将利用已知刚度的弹簧来确定质量（或重量）。根据弹簧的刚度（或弹簧常数），悬挂一定的质量将使弹簧延长一定的长度。正如胡克定律所描述的那样，物体越重，弹簧就越伸长。利用不同物理原理的其他类型的天平也存在。

Some scales can be calibrated to read in units of force (weight) such as newtons instead of units of mass such as kilograms. Scales and balances are widely used in commerce, as many products are sold and packaged by mass.

有些称可以校准，以牛顿等力（重量）单位读数，而不是千克等质量单位。称和天平广泛用于商业，因为许多产品都是按质量销售和包装的。毫牛和微牛是力的单位，马顿不是。

The positioning of satellites requires higher and higher precision as new space missions are developed. Precision is needed both in attitude control, for target pointing, and in position control, for absolute positioning in drag-free experiments, or relative positioning in formation flying. Because of the higher accuracy and resolution needed, and the lower mass of some scientific satellites, thrusters with performances on the order of 1 µN are currently needed.

随着新的空间任务的发展，对卫星定位的精度要求越来越高。在姿态控制、目标指向和位置控制中，无阻力实验中的绝对定位或编队飞行中的相对定位都需要精度。由于需要更高的精度和分辨率，以及一些科学卫星的质量较低，目前需要性能约为1µN的推进器。ONERA has been developing a micronewton balance since 1999. The ONERA micronewton thrust balance consists of a vertical pendulum [摆] that is allowed to rotate with respect to a structure that supports it.

In China, the earliest weighing balance excavated was from a tomb of the State of Chu of the Chinese Warring States Period dating back to the 3rd to 4th century BC in Mount Zuojiagong near Changsha, Hunan. The balance was made of wood and used bronze masses. 在中国，最早的天平出土于中国战国时期楚国墓，可追溯到公元前3至4世纪，位于湖南长沙附近的左家公山。天平由木头制成，使用青铜块。

Set of balance scales, with weights; Market hawker [小贩] weighing meat (in catty) on a beam balance, Malaysia (1969); A spring scale in Hong Kong

The catty, kati or jin (commonly in China), symbol 斤, is a traditional Chinese unit of mass used across East and Southeast Asia, notably for weighing food and other groceries in some wet markets, street markets, and shops.