A simple technique is described for the control and determination of the oxygen stoichiometry between 6.95-5.83 of pure deoxygenated YBa 2Cu 3O 7-δ (YBCO). By studying samples prepared using this method, two anomalous properties, namely (1) the step-like increase of the c-axis length of the crystal unit cell, and (2) the changes of the superconducting (SC) transition temperature, Tc, clearly showing the presence of two familiar plateaus as oxygen is gradually removed from YBCO have been reproduced. These two properties, first observed by Cava et al. by a Zr gettering technique thus appear to be inherent to pure YBCO. In addition, it is also found that the crystal structure of YBCO does not break down for an oxygen stoichiometry as low as 5.83. The extra (0.17) O atom per unit cell difference between 6.0 and 5.83 is believed to be lost from the O(4) sites. The technique adopted in this study which involves isothermal vacuum annealing (VA) can, therefore, be used as an alternative to the Zr gettering method for tuning various amounts of oxygen per unit cell in YBCO.