Up to now, no model or contactless sensor has been available for on-line control of the effectiveness of the flow of the stirring gas in the ladle in secondary metallurgy. A new method, based on the use of conoscopic holography, has been developed by Arcelor-Aceralia. It measures on line the vibrations in the walls of the ladle and relates them to the argon flow rate. This method is useful for determining the real state of the stirring process, obtaining an accurate index of the process of melt agitation that influences the composition homogeneity and cleanliness.