The Concept2 model B rowers came with a 13 tooth and 15 tooth cog. The Model C/D/E's come with a 14 tooth cog. This makes rowing comparisons between the models difficult for rowing competitions, Crossfit, training etc. This calculator takes the drag factor of a source rower and shows the comparable drag factor for another rower.
A headunit capable of calculating drag factor, such as the PM3 or PM4 is required.
To see Drag Factor go to More Options > Display Drag Factor and do about 6-7 pulls.