Use of plotDeltaDistribution() to assess the quality of automatic annotation of scRNA seq data

Question

[applepie]

Hello, I attempted to use the SingleR function to automatically find out the cell types of each scRNA seq clusters. After that, I use the plotDeltaDistribution() function to assess the quality of automatic annotation. From the attached photo, may I know how these graph be interpreted? I really have no idea about it. It would be nice if someone can explain it! Thanks.