The example is a good one, you are just misunderstanding what the problem is. Here is the synopsis: 1. User makes an appointment for 11am local time when he me

The example is a good one, you are just misunderstanding what the problem is. Here is the synopsis: 1. User makes an appointment for 11am local time when he meets his friend in Chile. Using current timezone rules (GMT-3), the program saves this in the database as 1400 UTC. 2. Chile decides to change the rules for their time zone. Software gets updated with new table. Now, the appointment is at 10am local time in Chile, since they are GMT-4 now (1400 UTC = 10am GMT-4)