A pairwise comparison is a process where you take two things and compare them. In this context, we look at pairs of criteria at a time to see which one is harder. By repeating this process we eventually figure out the relative difficulty of different criteria.
Turning a developmental rubric from this:

Into this:

Here’s a video all about it:
Here is me conducting a pairwise comparison for the VCAA Year 12 History Performance Descriptors. In this example, each post-it colour represents a new skill. The rubric itself goes from left to right instead of bottom to top. You will note that this has 9 skills and more than 15 criteria for some skills. This is way more than you would ever want to have for an individual assessment task, but in this example, it was for a whole Area of Study for Year 12. Obviously the video is sped up – I think this probably took me about 1.5 hours. I would recommend doing a pairwise comparison with 1-2 other people. It is really good if there is at least one experienced pedagogical subject matter expert (e.g. someone who has been teaching the subject) and an assessment expert.