High quality pH sensor allows reliable readings easily. The pH for this sensor is not at 0V for pH7; it's around 2.51V from the multimeter and 3.03V at pH4. If calculated, 2.51 - 3.03 = -0.52. The difference between pH4.01 and pH7 is 2.99. The device works perfectly for a variety of applications such as lab work, DIY projects, test circuits, gardening, and fish tank monitoring. There is abundant information available online regarding its use and compatible codes for various applications. The device requires minimal maintenance and cleaning, and comes with a protective case to ensure safe and long-term operation. Color: As shown Material: Plastic + Metal Package Contents: 1 x pH test module 1 x pH probe Only the above package content is included; other items are not part of the package. Note: Light reflection and differences in display screens may cause slight variations in color between the image and the actual item. Measurement error allowance is +/- 1-3 cm.