Of the two axes in the oxygen binding curve, the y-axis shows the of the two axes in the oxygen binding curve, the y-axis shows the blank, where the percentage of bound and unbound oxygen binding sites can be determined. an axis value of 0.4 means that 40% of hemoglobin oxygen binding sites are blank to oxygen within the sample (ex. blood sample). conversely, this also signifies that 60% of those available oxygen binding sites are blank to oxygen., where the percentage of bound and unbound oxygen binding sites can be determined.