One of the main tools a grower will need, soil meters can test for a number of parameters. If you are growing in soil, a meter or test kit is an absolute must to ensure you are growing in a proper environment.
What does a soil test kit tell you?
The most basic soil test kits will determine the pH of the soil. Plants need a pH of between 5-6.5 in order to absorb nutrients, and if your soil is preventing this from happening, it needs to be corrected using a pH supplement. Another thing some soil meters can test for is moisture. Growers sometimes like to cycle the soil between very moist and very dry to active certain processes, and using your finger to guess how damp your soil is can prove ineffective.
More advanced, multi-use tools can also test for specific macronutrient profile in the soil, also known as NPK. This test reveals how much nitrogen, phosphorus, and potassium are in the soil, and you can adjust these nutrients to line up with your goals and the plants current stage.