 possible values. It makes the work of a decision circuit really easy. Such a circuit has to decide on just one of two possibilities. Look at real life: A light is on or it is off; two values, on and off. A car engine is running or not running, and SO on. In our case of interest, we denominate one value a 1 and denominate the other a 0. We could have a condition where current flows, and we'll call that condition a 1; no current flowing we'll call a 0 (Ref. 3).³ 3 The reader with insight will note an ambiguity here. We could reverse the conditions, making the 1 state a 0 and the 0 state a 1. We address this issue in Chapter 10. 2.5 INTRODUCTION TO TRANSPORTING ELECTRICAL SIGNALS Of course we are defining a binary system with a number base of 2. Our day-to-day numbers are based on a decimal number system where the number base is 10. There is a review of binary arithmetic in Appendix B. The basic key in binary digital transmission is the bit, which is the smallest unit of information in the binary system of notation. It is the abbreviation of the term binary digit. It is a unit of information represented by either a "1" or a "0." A 1 and a 0 do not carry much information, yet we do use just one binary digit in many applications. One of the four types of telephone signaling is called supervisory signaling. The only information necessary in this case is that the line is busy or it is idle. We may assign the idle state a 0 and the busy state a 1. Another application where only a single binary digit is required is in built-in test equipment (BITE). In this case, we accept one of two conditions: A circuit, module, or printed circuit board (PCB) is operational or it is not. BITE automates the troubleshooting of electronic equipment. To increase the information capacity of a binary system is to place several bits (binary digits) contiguously together. For instance, if we have a 2-bit code, there are four possi- bilities: 00, 01, 10, and 11. A 3-bit code provides eight different binary sequences, each 3 bits long. In this c