Answer:
After entering a time in 24-hour format, this calculator lets you add and subtract a period to give a new time, also in 24 hour format. The 24 hour time format is also known as "military time".
For example, you could enter the time 15:00:00 (3 pm), then add 70 seconds to it which would give 15:01:10 ( 3:01 and 10 seconds pm).