A useful trick for determining the accuracy of CG-locating softward is to plug in the dimensions of a successful canard (tail first) airplane, just to see the whether the algorithm gets totally confused, or takes it in stride. Da Rock's suggested program, copied below, failed miserably, unless I screwed up in some way, so I must conclude that it contains significant errors, not only for canards, but for conventional configurations. Maybe someone else could throw a canard at it, and see how it handles it. A good program should be able to work out the distribution of lift of a canard, as well as a normal layout, sufficiently accurately to locate the CG. If not, it is probably in error in calculating the effect of downwash on tail lift.

http://www.geistware.com/rcmodeling/cg_super_calc.htm