It is up to the teachers to document the seat number in a suitable manner.
The seat number can be written down on the test sheet itself or it is entered in a registration list as recommended in the guidelines.
However, it is important that the number is correctly noted, in order to find out which student was sitting on which place in case of need.
The numbering of the seats in the lecture hall corresponds to the numbering in the occupancy-plans for presence-exams on the Room Information page.
You can find more information on presence-exams in the Guideline for Presence Exams at TU Wien.