We typically see power numbers from the oarlock equate to 85% of ERG values but this varies slightly. In all three systems, WORK is calculated as FORCE over the LENGTH of the stroke. POWER is WORK over time. These are measured as the actual output of the athlete applied to the oar/handle and should be fairly equivalent. Work done by the athlete on the slide is not measured in either case, although it does affect the athlete/boat/oar system. Note that calories on the C2 erg are calculated differently as there is a "per stroke" addition for calories burned going up the slide standardized for a 175 pound male athlete.