e National Institute of Standards and Technology (NIST) and the Alliance for Telecommunications Industry Solutions (ATIS), held somewhere in North America (up until re- cently, it was held annually in San Jose). The topic areas are much the same as those for ITSF. Although many of the timing experts attend both, the WSTS tends to have more of an American flavor. See https://wsts.atis.org/ for details. WSTS is usually held between March and May every year, with the schedule alternating to line up with the ITU-T Q13/15 interim meetings held in North America. This allows ITU-T deleg- ates to attend and present at the conference as part of a single business trip. Of course, with the COVID situation at the time of writing, that is less of a concern, and conferences are presumed to remain virtual for the next while. So, now that you have written the RFP, selected a shortlist of possible vendors, and perhaps atten- ded a few conferences, the next step is to run a test event, a proof of concept (POC) to validate the offered equipment. This launches the whole area of testing timing, which is quite a specialized area of expertise, SO this chapter uses several of the following sections to cover it comprehensively. 12.3 Testing Timing One of the first times that many engineers, newly introduced to timing, realize the difficulty of the whole topic of synchronization is when they first go into the lab and conduct testing. There is dizzying number of testing options available, and you need a fair deal of background knowledge be- fore starting in the lab. Well, to rephrase that, you should have substantial background knowledge before starting, but the experience of the authors suggests many engineers do not have sufficient knowledge to conduct testing. This leads to a high probability for unsuccessful tests, or at the very least, frustration and even public embarrassment. This lack of background knowledge is the main reason that this chapter includes a separate section on testing timing. There actually is a copious amount of edu