Your T-number is a unique identification number and and it will never change. It is in the format of capital "T" followed by eight digits (for example, T12345678).
Your T-number is normally not used for logging into ATU systems. It is used primarily for identification and record keeping.
You can find your T-number printed on your ATU identification card at the bottom. It is also printed on several OneTech pages (such as your transcript or schedule). You can also find out your T-number by contacting the Campus Support Center, the Admissions Office, the Registrar's Office or the Human Resources Office.