Model has a single factor ("treatment") with three levels, and a single continuous covariate "x". User can adjust population means of treatment levels, error variance, and sample size. User can also create an interaction and adjust slope of covariate separately for all three treatment levels. Independently of this, user can choose to fit an ANCOVA with or without interaction, or leave out the covariate altogether by fitting a one-way ANOVA. User can add fitted lines or population lines to the data plot; the image above demonstrate fitting a "no interaction" model in the presence of an interaction.