A student used a volumetric pipet to measure the volume of the vinegar sample. The vinegar sample was titrated with NaOH and the acetic acid concentration was determined to be 4.20 %mass. For the second titration, the student used a graduated cylinder to measure the vinegar sample. The student calculated the concentration to be 4.30% mass. In which experiment should the student be more confident of the concentration of the acetic acid? Why?