Test Tube pH PensFits standard test tubes 16 x 50 mm or larger. Highly stable and accurate readings with a large LCD display. Designed for simple one hand operation. Automatically calibrates to pH 4, 7 and 10 buffers and can be adjusted to recognize some other non standard buffers as well. Features hold function, and auto power off with low battery indicator. General Purpose Glass Probe: EPA compliant for labs and wine Penetration Probe: for food & soil Flat Tip