In Searle's experiment to determine the young's modulus of a wire. The diameter of the given wire is measured by using

Question

$(a)\;\text { the micrometer screw after air bubble in the spirit level is brought to the centre.} \\(b)\; \text { the micrometer screw after loads are added to the weight hanger}\\(c)\;\text{using the screw gavge} \\(d)\;\text { using the vernier calliper provided .}$