Manual and semi-automatic colony counters rely on technicians to mark colonies on the plate's exterior with a specific pen, and the device tracks these markings.Additional features include a graticule, segmentation disc, and centering adapters, along with options for darkening the background, glare-free illumination, and an integrated averaging tool for multiple plate counting.The working principle involves placing a Petri plate on an electronic pressure pad with light illumination, tapping each colony with the auto marker probe pen to mark it, and registering the count on the digital display.Parts and functions of manual colony counters include an auto marker probe pen, which registers counts with an audible beep and updates the count on a digital display.