Decibels, directionality and attenuation decide where an inspector stands and what a reading means, so the book teaches them properly and works the arithmetic: what a 13 dB rise actually is, how to subtract a background, and how much of a reading is lost across a walkway.
The instrument’s own controls get a chapter, because tuning, gain and filtering are what an inspector touches all day and what makes one reading comparable with the next.
Study material written by Sensemore. It is not accredited training, it is not from any certification body’s question bank, and it confers no certification.