Unlike most other non-combat sports, rowing has a special weight category called lightweight (Lwt for short). According to FISA, this weight category was introduced "to encourage more universality in the sport especially among nations with less statuesque people". The first lightweight events were held at the World Championships in 1974 for men and 1985 for women. Lightweight rowing was added to the Olympics in 1996.
On theme with C2’s interchangeability, models D or E are essentially the same machine. When we talk about one we’re talking about both. The Concept 2 E is just 8 pounds heavier but is made out of stronger stuff all around — what’s plastic on the model D is aluminium on the model E, and what’s aluminum on the model D is welded steel on the model E. The only noticeable variations are seat height and display position.

If you’re interested in using a rowing machine for focused training — whether for outdoor rowing, an indoor competition, or as part of a larger fitness program — you’ll want air resistance. If you’re drawn to rowers for the enjoyability (alongside the full-body, cardio-plus-strength training efficacy) of a rowing workout, consider a machine with water resistance.
In sweep or sweep-oar rowing, each rower has one oar, held with both hands. This is generally done in pairs, fours, and eights. In some regions of the world, each rower in a sweep boat is referred to either as port or starboard, depending on which side of the boat the rower's oar extends to. In other regions, the port side is referred to as stroke side, and the starboard side as bow side; this applies even if the stroke oarsman is rowing on bow side and/or the bow oarsman on stroke side.