Your Pulse™ Meter uses radio frequencies to determine the pore conductivity in substrates. Electrical conductivity is a common measure of the nutrient ions present in a solution or substrate and is widely used as an indicator of available nutrients.
Electrical conductivity (measured in EC) is a measure of total ions present and cannot tell if nutrient levels are out of balance (e.g. too much nitrogen but not enough potassium).
The electrical conductivity in any substrate will generally be lower than the EC of the nutrient solution being added due to how substrates can buffer ions. Accurate EC measurements require at least 20% volumetric moisture content in the substrate.