Hi Karl, I think the reason is that EASA airworthiness requirements
stipulate a maximum allowable figure for the minimum cockpit load.
Manufacturers make sure that their glider complies with this and then
placard that maximum figure instead of bothering to work out the actual
figure for all cases. Some years back I took delivery of a new DG500, it
was placarded minimum front cockpit load 75 Kg (I think that was the
figure, it was a while ago). On weighing, and checking the C of G limits
in the flight manual, we found that a big pilot would actually be within
limits flying solo in the rear cockpit!

At 00:52 04 June 2014, Karl Striedieck wrote:
Anyone know why the Duo (and supposedly other Doppelsetzers) have the
same
minimum front seat weight with or without a person in the back seat?

The rear seat moment arm has about 1/4th the effect compared to the
front,
so I would think a 200 pounder in the rear would reduce the front min
weight by 50 pounds - nicht wahr?

Maybe the numbers are based on a super cautious approach for situations
like an instructor jumping out when the student solos and forgetting to
recompute the cg?