USA Swimming: Good vs Poor Core-Driven Backstroke Rotation

In this video, (slowed down to highlight the timing) you can see that the swimmer maintains connection between the components of their stroke and is able to keep their entry in line with their core. Increasing the pace of that core-driven rotation is how you should think about increasing your tempo.

In this video, you can see an athlete whose arms are working independently from their body, forcing the tempo without a matching rotational pace from their core. Notice how the right hand is entering while the body is still rotated to the left. This is a common mistake and can lead to a number of ancillary stroke flaws.