For those not in the know, rowing machines all have different calibrations. C2 is the standard because they're very consistent across machines and are by far the best made allowing for many thousands of hours of use without failures. Most experienced rowers won't touch anything other than a C2.
Edit: reading further, the 'moat' here appears to be electrically controlled 100lb high resistance settings. Be VERY careful with this. It's well established that most non-trained athletes will hurt themselves with this feature as it's a common trope on C2 machines. The rowing posture can be rather dangerous for high weight if misused.