Resistivity is the property of the material that resists the flow of electrons through it. SI unit of resistivity is ohm (Ω).
The experiment involves setting up an circuit that consists of a battery resistance an rheostat an voltmeter and ammeter. On variable resistance the reading of voltmeter and ammeter should remain constant that is equal to Resistance. 
R = V/I which remains constant
Hence resistance depends on area and length of the conductor