A spring balance is commonly used to "weigh" objects even though, in reality, it senses a different physical quantity.
(i) What physical quantity does a spring balance actually measure? State the relation between this quantity and the scale reading when the balance is calibrated in kilograms at the Earth’s surface.
(ii) Briefly describe the procedure by which the divisions on a spring balance are marked in kilograms even though the instrument itself is sensitive to the quantity named in part (i).
(iii) The balance is taken to the summit of a mountain where the local value of g is 9.70m s−2. When a 5kg standard mass (as verified on a beam balance) is suspended from it, what number will the pointer indicate on the kilogram scale? Explain your reasoning clearly.