Standard frequency in the US is 60 hertz, actually I think in the US on the mainland, US main continent, there are three different synchronous areas.

美国的电流标准频率是60赫兹，实际上我认为在美国大陆有三个电流频率相同的不同地区。

The technology is getting to the point now where that microwave frequency isn't precise enough for the applications that require precise time, so we are now working to develop optical frequency standards.

这项技术现在已经到了微波频率对于需要精确时间的应用来说不够精确的地步，所以我们现在正在努力开发光学频率标准。