<P> Spring scales have two sources of error that balances do not: the measured mass varies with the strength of the local gravitational force (by as much as 0.5% at different locations on Earth), and the elasticity of the measurement spring can vary slightly with temperature . With proper manufacturing and setup, however, spring scales can be rated as legal for commerce . To remove the temperature error, a commerce - legal spring scale must either have temperature - compensated springs or be used at a fairly constant temperature . To eliminate the effect of gravity variations, a commerce - legal spring scale must be calibrated where it is used . </P> <P> It is also common in high - capacity applications such as crane scales to use hydraulic force to sense mass . The test force is applied to a piston or diaphragm and transmitted through hydraulic lines to a dial indicator based on a Bourdon tube or electronic sensor . </P> <P> A digital bathroom scale is a type of electronic weighing machine, which is used to measure many readings including body fat, BMI, lean mass, muscle mass, water ratio along with body mass . The digital bathroom scale is a smart scale which has many functions like smartphone integration, cloud storage, fitness tracking, etc . </P> <P> In electronic versions of spring scales, the deflection of a beam supporting the unknown mass is measured using a strain gauge, which is a length - sensitive electrical resistance . The capacity of such devices is only limited by the resistance of the beam to deflection . The results from several supporting locations may be added electronically, so this technique is suitable for determining the mass of very heavy objects, such as trucks and rail cars, and is used in a modern weighbridge . </P>

Which instrument is used to measure the weight of the body