A laboratory-developed HPLC method is employed to determine the amount of additive in diesel oil. 0.5mL of sample is loaded onto an extraction cartridge containing 3.5g mass of silica. 20mL of hexane is first used to elute the diesel oil at a rate of 3mL/min. Then the additive is eluted at a rate of 2.0mL/min with 10mL of butanol in hexane (5%v/v). The eluted additive is then injected into the HPLC for quantitation. Since the present method is not a standard method, ruggedness test has to be carried out. Describe in details how the ruggedness test can be conducted in its own laboratory