HDE Hydroponic Fruit Vegetable Grow Kit- 3-in-1 Soil Light Sensor + TDS ppm Test Pen + pH Meter Digital Monitor Simple and easy to use, insert the probe into the soil, switch the setting and read the scale No batteries required; Probe length ~ 18cm Can be used for indoor and outdoor flowers & plants, fruit & vegetable gardens, and lawns; The perfect tool to test soil conditions with high accuracy and easy operation TDS Tester Measures 0-9990 parts per million; **Note: Calibration fluid is needed, but not included with this product For measurements over 999 ppm, the LED indicator flashes 10x | Temperature Range: 0-80 C (32 - 176 F)