What is my Octane Score?

Your Octane Score is effectively a proxy for VO2 Max.

Clinical studies of CAROL have shown that increases in octane scores correlate with increases in VO2 max. For reference, VO2max is the measurement of the maximum amount of oxygen a person can utilize during intense exercise.
Your Octane Score measurers your power per heart beat. It is a measurement of how strong your heart is. Higher scores are typically better but please note that it's relative. I wouldn't read too much into it if your score fluctuates slightly!