世界 时钟

一、怎么用

1. 在搜索框输入国家名或城市名（中英文都可以，例如"日本"、"Tokyo"）；
2. 从下拉框里选一个具体地点，点「添加到仪表盘」；
3. 仪表盘会每秒刷新，点卡片上的删除即可移除；
4. 你的选择保存在当前浏览器里，下次打开自动恢复。

二、为什么有些国家有好几个"代表城市"

因为一个国家不一定只有一个时区。美国本土跨四个时区，澳大利亚跨三个，俄罗斯跨九个以上。这时只给一个"国家时间"就是错的，所以工具会列出代表城市，由你选择真正关心的那个。

常见用途：和海外同事约会议、盯美股开盘、给异地家人打电话前先看一眼对方是不是深夜。

三、时间是怎么算出来的

整个过程不联网校时：浏览器本身带了一份 IANA 时区数据库，工具用 Intl.DateTimeFormat 把当前时刻按目标时区格式化。因此：

• 夏令时（DST）自动处理。北美、欧洲等地区每年切换两次，切换当天的时间偏移会变，工具跟随系统时区库自动调整。
• 准确性取决于你的系统时间。如果电脑时间本身偏了，这里显示的所有时间都会一起偏。要精确到秒，请确认系统开启了自动校时。
• 不涉及任何定位。工具不会读取你的地理位置，也不会上传你添加的城市。

四、几个容易混淆的地方

时区不是"整点偏移"。印度是 UTC+5:30，尼泊尔是 UTC+5:45，不是所有地方都按整小时划分。

缩写有歧义。CST 可以指中国标准时间、美国中部时间，也可能是古巴标准时间。跨时区沟通时，写出"UTC+8"比写缩写安全得多。

跨日界线要看清日期。北京上午 9 点时，洛杉矶还是前一天下午 6 点。安排会议时以"哪一天"对齐，比只看钟点更不容易出错。

How to use it

1. Type a country or city into the search box — Chinese or English both work;
2. Pick a specific location from the dropdown and press Add to dashboard;
3. The dashboard refreshes every second; remove a card with its delete button;
4. Your selection is stored in this browser and restored next time.

Why some countries get several cities

Because a country does not necessarily have one time zone. The contiguous United States spans four, Australia three, Russia nine or more. A single country time would simply be wrong, so the tool lists representative cities and lets you choose the one you actually care about.

Typical uses: scheduling calls with overseas colleagues, watching a market open, checking whether it is the middle of the night for family abroad.

How the time is computed

No network time service is involved. Your browser ships an IANA time zone database, and the tool formats the current instant with Intl.DateTimeFormat. Consequently:

• Daylight saving is handled automatically. North America and Europe switch twice a year; offsets follow your system's zone data.
• Accuracy depends on your system clock. If your machine is off, every clock here is off by the same amount. Enable automatic time sync if seconds matter.
• No geolocation. The tool never reads your location and never uploads the cities you add.

Easy confusions

Offsets are not all whole hours. India is UTC+5:30, Nepal UTC+5:45.

Abbreviations are ambiguous. CST could be China Standard Time, US Central, or Cuba Standard. Writing UTC+8 is always safer across time zones.

Watch the date, not just the hour. When it is 9 a.m. in Beijing it is still 6 p.m. the previous day in Los Angeles. Agreeing on which day first prevents most scheduling mistakes.