This special staining tray maintains slide surface in exact horizontal position for layering & maintaining the reagents on it during staining procedure. It accommodates four slides. It is also easy to drain off the reagents without disturbing other slides.
Because of its exact horizontal position the smear is stained evenly.
Also as only the required amount of reagent is used, there are no remnant deposits occurring at the bottom & no likely changes in pH as seen in vertical staining procedure