Hello again, sorry for bombarding you with mails... when I tried to link astlib with slalib, I get ../.libs/libast.so: undefined reference to `slaPvobs' palSlaPvobs is used in ast/specmap.c. In slalib, a Fortran subroutine "sla_PVOBS" exists, and a C function "slaPvobs" is declared in slalib.h, but not defined. Probably it is just forgotten in sla.c? Could you add this function there? It does not look too complicated to do it myself, however... Best regards, and have a nice weekend Ole