The perpetual calendar complication displays the day, date and month, but it requires less adjustment than an annual calendar. This complication knows the number of days in each month but it also knows the year so that it will automatically adjust for leap year. The next time a perpetual calendar will have to be adjusted is in the year 2100.
Watches featuring a GMT complication (which stands for Greenwich Mean Time) can display a second time zone thanks to an additional hand. They are much appreciated by travelers and airline pilots.
The power reserve indicator tells you the time the watch will continue to function. It can either be seen on hand winding or automatic watches.
A day date watch displays the days of the week (from monday to sunday) and the date (between 1 and 31).
The date is a small window on the dial which indicates the day of the month (between 1 and 31).
Watches featuring a small seconds have a smaller subcounter, usually located at 6h, which indicates seconds.