High quality pH sensor allows reliable readings easily. The pH for this sensor is not at 0V for a pH7; it's around 2.51V from the multimeter and pH4 at 3.03V. If you calculate, 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 integration with various applications. The device requires minimal maintenance and cleaning, and includes a protective case to ensure long-term safe and operational condition. 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 included. Note: Light reflection and different display settings may cause slight variations in color between the image and the actual item. Measurement error allowance is +/- 1-3 cm.