4 in 1To check the quality of your water, whether it comes from a faucet, hot tub, home brew, indoor soil, aquarium, of a hydroponics or a swimming pool.In addition, the PH tester pens are of small size, lightweight and easy to carry when you go out. High AccuracyThe pH meters range from 0.00 to 14.00 (PH). PH resolution is 0.01pH, accuracy 0.01pH, blue backlit LCD display for reliable and fast readings. EASY TO CALIBRATEThe pH tester self-calibrates at three points). You don't need any tools; simply remove the protective cap and immerse the pH meter electrode in the solution. Press "ON/OFF" to turn on the electronic pH meter, swirl gently and wait a few seconds until the reading stabilizes. EASY TO USEThe pH tester has a self-calibrating feature so you can get a reading quickly. Wide ApplicationsA single calibration powder can be easily stored in a drawer, bag or suitcase for easy portability. It is ideal for testing pH balance in drinking water, aquariums, swimming pools, spas or hydroponics.