The number indicated by /500m is referred to as your split time. It is an estimation of how much time it would take you to row 500 meters if you maintained the exact same level of speed of your current stroke. Essentially, it functions as the most direct measure of how much work you are doing at any given time. The lower your split is, the harder your body is pushing--so in other words, the faster you are estimated to complete 500 meters.
Another useful form of measurement is your watts generated, and you will see that number go up and down as you row depending on how much power you are exerting on each stroke. The watts metric refers to the average amount of power generated per stroke. It is the most literal measurement of the amount of power you are exerting on Hydrow. High watts are often correlated to low splits, but the relationship between the two isn’t always one being the product of the other.