A common bathroom floor scale which measures the force with which a body is pulled toward the earth. This scale displays both weight in pounds and mass in kg.

Zero the scale using the dial on the bottom.

Sources of error

• Friction in the moving components that causes the scale to reach equilibrium at a different configuration than a frictionless equilibrium should occur.
• Misaligned mechanical components due to thermal expansion or contraction of components.
• Magnetic fields acting on ferrous components.
• Forces from electric fields, for example, from feet shuffled on carpets on a dry day.
• Gravitational differences.
• Vibration and seismic disturbances.
• Buoyancy – Objects in air develop a buoyancy force that is directly proportional to the volume of air displaced. The difference in density of air due to barometric pressure and temperature creates an upward force.
• Air gusts which push the scale up or down.