In a vernier calliper if the vernier is on the right side of the zero of the main scale and nth vernier scale division coincides with main scale division correct reading is

Question

$(a)\;\text{observation reading - n $\times$ least count} \\(b)\;\text {observation reading + n $\times$ least count} \\(c)\;\text{observation reading $\times$ least count} \\(d)\;\text{none}$