Hello all,
I think it might cause a little confusion and breaks the orthogonality of the design of the various thorns. I would prefer to leave the default as it is now, i.e. an empty list of variables, rather than couple it to WeylScal4, which is an unrelated (except by common use) thorn. Of course, this isn't a hugely important point, so If there is strong support for Roland's suggestion, I would accept the view of the majority :)
Either option is fine by me.
I think having Parameter files that actually mention the variable that is acted on is not a bad idea after all. It seems as if there are only AHFinderDirect (uses Spacemask) and SetMask_SphericalSurface (uses HydroBase::hydro_excision_mask) that mention other thorn's GF in their parameter file. Since Multipole is an infrastructure thorn it probably makes sense for it *not* to refer to the specific physics thorn WeylScal4. I retract my suggestion of a default value :-)
Yours, Roland