The Drummond Scientific Co. Portable Pipet-Aid XP, Cat. No. 4-000-101, is smaller and lightweight, specifically designed to minimize operator fatigue. It accepts most pipettes from 1 to 100 mL. Depressing the top button fills the pipet, depressing the lower button empties it. The flow rate is proportional to the amount each button is depressed. Each button has three speeds, F Fast, M Medium, S Slow. The medium speed is suitable for most routine techniques. Fast can be used for rapid filling of large pipets or breaking up cell clumps. Slow speed is ideal when using small pipets or when more precise delivery is required.