To calculate time in Tianshui, Gansu, you need to consider the time zone difference. Tianshui is located in the China Standard Time (CST) zone, which is 8 hours ahead of Coordinated Universal Time (UTC+8). Therefore, when you want to calculate the time in Tianshui, you simply add 8 hours to the UTC time. For example, if it is 12:00 PM (noon) in UTC, it will be 8:00 PM in Tianshui.

The reason for this time difference is due to the country's geographical location and the historical decision to adopt a single time zone for the entire nation. China spans five time zones, but to simplify matters and promote national unity, the government chose to use a single time zone, which is UTC+8. This means that all regions, including Tianshui in Gansu province, follow the same time as Beijing, the capital city.

According to data from the China Standard Time official website, the country's time zone policy has been in place since 1949, and it has been consistently applied across the nation. This has helped to streamline transportation, communication, and business operations, as all regions operate under the same time frame. The decision to adopt a single time zone was also influenced by the country's vast size, which makes it impractical to have multiple time zones.

In conclusion, to calculate the time in Tianshui, Gansu, you add 8 hours to the UTC time. This policy is a result of China's historical decision to adopt a single time zone for the entire nation, which has been in place since 1949.