The use of joint ternaries with size and color coding provides a concise means of interpreting the large quantity of data from automated feature analysis (AFA) and observing the inclusion population at different stages of steelmaking. A method was developed and applied to study the effect of mill practice such as tap practice; live vs kill-on-tap, desulfurization method, heat sequence number, and liquid steel transfer on the inclusion population. Samples for analysis were collected from two industrial steel mills. Results show the formation of spinel inclusions with long holding times in the ladle and also killing-on-tap. After calcium treatment, spinel inclusions were partly and fully modified. Also observed was the formation of CaS and MgO rich inclusions. Analysis of tundish samples showed evidence of reoxidation and also the ability of CaS inclusions to act as a buffer for reoxidation inclusions.