很多业余无线电爱好者在使用CW模式通联结束时，都会加上2个点做为结束语，其实这种操作还是一个火车拉来的礼仪。
在过去的日子里，每一列火车在离开车站的时候，都会发出两声短促的汽笛声用来提醒每个人它要离开。有一些接触过这些做法的老报务操作员就把这种操作运用在了自己的通联过程中，在每一段通联的结束时使用，用来表达“再见”。
由于这种操作非常简单和方便，在通联结束时很有特点，而且不会降低通联的效率，最终被业余无线电爱好者广泛使用在彼此的CW模式通联结束语中。
这种操作在业余无线电圈子里一直被保留到了现在。
下面是一段真实的历史记录了以前的业余无线电爱好者的经历：ERIC, K1NUN writes "When I was first licensed in the early 1960s, we ended our CW conversations withdi dididi di (Shave and a haircut) to which the other station would reply di di (two bits). Then station 2 sentdi dididi di and the first would reply di di. Sometimes, and particularly among us young teenagers, this reparte might continue for several minutes. Over time, this back and forth terminal handshake shortened just to di di. Also, about that time, sometimes instead of calling CQ, one would just go di dididi di over and over on a frequency (remember, we were crystal controlled in the novice bands) while tuning the receiver, listening for anyone who sent a synchronized di di. After enough back and forth to ensure proper syncronicity, one of the stations would send QRZ? (with the question mark so as to really ask who is calling me). Thus, dit dit also began a QSO in some cases. Fortunately , this custom died within a very few years as the rules changed and more of us could use transceivers that put us right on frequency and we did not have to tune around and search for responders And that's my story and I lived it.
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