During a study of gas exchange in high-altitude birds, a physiologist compares the oxygen dissociation curve of bar-headed goose (Anser indicus) haemoglobin to that of lowland greylag goose (Anser anser) haemoglobin.

The lowland goose haemoglobin dissociation curve is defined by the following reference points:

• At a partial pressure of ${pO}_2=30mmHg$, lowland goose haemoglobin is $50\%$ saturated.
• At a partial pressure of ${pO}_2=50mmHg$, lowland goose haemoglobin is $80\%$ saturated.
• At a partial pressure of ${pO}_2=80mmHg$, lowland goose haemoglobin is $95\%$ saturated.

The physiologist models the oxygen dissociation curve for bar-headed goose haemoglobin as follows:

1. At low oxygen levels, the saturation of bar-headed goose haemoglobin increases linearly at a constant rate of $4\%$ per $mmHg$ of oxygen, starting from the origin $(0,0)$, up to a saturation level of $80\%$.
2. At higher partial pressures of oxygen, the rate of oxygen binding slows down gradually until bar-headed goose haemoglobin reaches $100\%$ saturation.
3. The partial pressure at which bar-headed goose haemoglobin first reaches $100\%$ saturation is equal to the partial pressure at which lowland goose haemoglobin is $80\%$ saturated.

Based on this model: