#4: Time Management
The 24-hour time-keeping system has become fairly standard globally, with few exceptions. Unfortunately, some use the 12-hour system, which can cause confusion for both those living in the countries that follow it and for those from outside.
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Only 18 countries in the world use the 12-hour format unless it is related to something like a military operation. The ambiguity of the 12-hour system can be not just confusing but dangerous in certain circumstances. This story is proof of just how confusing it can get.