Investigations of the Δαδ error in the FK4, based on Astrolabe observations made at “Félix Aguilar” Astronomical Observatory in San Juan, Argentina and compared with that made vvith other instruments (Astrolabe and Repsold Meridian Circle at Cerro Calán, Chile, and Astrolabe at Tananarive, Madagascar), gave similar results. This would clearly indicate that the curves are due mainly to an error of Δαδ type in the FK4 right-ascension system and not to instrumental error or personnel or local effects.