Page authority is a model used to predict the ranking of a single page of the domain. The higher is the page authority, the more is the potential for the domain to attain higher ranking on search results. Page authority is also measured in the same way as the domain authority.
Domain authority is measured by the scores on the scale. It is a logarithmic scale which ranges from 0-100. The points are given out of 100. The higher the score, the more is the potential for the individual page to rank well on that domain.