High quality PH sensor at a convenient price, allows reliable readings easily. The PH for this sensor is not at 0v for a PH7 it's around 2.51v from the multi-meter and PH4 at 3.03. 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, test circuits, gardening and fish tank applications, among many others. There is also abundant information on the Internet about its use and codes associated with different applications. The device requires minimal maintenance and cleaning measures, with a protection box, which allows it to be in a safe and operational condition for a long time. Color:As Shown Material:Plastic+Metal Package Contents: 1 * PH test module 1 * PH probe Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.