 receiving device is 5% slower or faster than the transmitting device. Only 40% (5 X 8) timing error accumulates, well inside of the 50% maximum. Remember that the sampling takes place at mid-bit position of 50% of its timing interval. Minimum lengths of stop elements vary, depending on the convention used on a partic- ular network. In the commercial world, the stop element can be one or two unit intervals (bits) duration. With some older systems, the stop element was 1.42 unit intervals dura- tion. In military operation the stop element is 1.5 unit intervals long. The start space is always 1 unit interval duration. As we are aware, a primary objective in the design of data systems is to minimize errors in a received bit stream or to minimize the error rate. Two of the prime causes of errors are noise and improper timing relationships. With start-stop systems a character begins with a mark-to-space transition at the beginning of the start-space. Then 1.5 unit intervals later, the timing causes the receiving device to sample the first information element, which is simply a 1 or 0 decision. The receiver continues to sample at one-bit intervals until the stop mark is received. It knows a priori where (when) it should occur. In start-stop systems the last information bit is the most susceptible to cumulative timing errors. Synchronous data transmission is another story altogether. It is much more efficient because it does not have start and stop elements, which are really overhead. Synchronous data transmission consists of a continuous serial stream of information elements or bits, as illustrated in Figure 10.5. With start-stop systems, timing error could only accumulate inside a character, the eight bits of the example given previously. This is not SO for synchronous systems. Timing error can accumulate for the entire length of a frame or over many frames. With start-stop systems, the receiving device knows when a character starts by the mark-to-space transition at the start-space. In a synchronous transmission syst