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## 1     INTRODUCTION

What is meant by frequency and why is it more fundamental than time?

The only mathematics you need to begin with is the ability to count and to perform the basic arithmetical operations of multiply and divide.

### 1.1 Frequency. Hertz.

The unit of frequency is the hertz. Your heart rate is near to one hertz.

Let’s start with the idea of frequency. (Rate means the same thing.) Frequency is a key concept and this book is built on it.

Take your pulse. Its frequency is about one hertz. This book is all about things that happen at a much greater rate, at about one terahertz. I will define a terahertz a little later, but for now it is enough to know that it is a rate. Let’s begin with something closer to hand, the rate at which your ...

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