answer:“A spring scale measures weight by the distance a spring deflects under its load. A balance compares the torque on the arm due to the sample weight to the torque on the arm due to a standard reference weight using a horizontal lever. Specialized medical scales and bathroom scales are used to measure the body weight of human beings. The balance (also balance scale, beam balance and laboratory balance) was the first mass measuring instrument invented. There has been a recent trend to “digital load cells” which are actually strain-gauge cells with dedicated analog converters and networking built into the cell itself.” “Some of the sources of error in high-precision balances or scales are: * Buoyancy, because the object being weighed displaces a certain amount of air, which must be accounted for. Some high-precision balances may be operated in a vacuum. * Error in mass of reference weight * Air gusts, even small ones, which push the scale up or down * Friction in the moving components that cause the scale to reach equilibrium at a different configuration than a frictionless equilibrium should occur. * Settling airborne dust contributing to the weight * Mis-calibration over time, due to drift in the circuit’s accuracy, or temperature change * Mis-aligned mechanical components due to thermal expansion/contraction of components * Magnetic fields acting on ferrous components * Forces from electrostatic fields, for example, from feet shuffled on carpets on a dry day * Chemical reactivity between air and the substance being weighed (or the balance itself, in the form of corrosion) * Condensation of atmospheric water on cold items * Evaporation of water from wet items * Convection of air from hot or cold items * Gravitational anomalies for a scale, but not for a balance. I.e. using the scale near a mountain; failing to level and recalibrate the scale after moving it from one geographical location to another) * Vibration and seismic disturbances; for example, the rumbling from a passing truck” Wikipedia