You could be a school student or even a member in an important conference. At big universities, the classrooms are recorded for academic purposes and you will be given a copy of everyday's class for better comprehension. However, in the eventuality of an absence of such a facility, do not hesitate to take out your smartphones and record the lessons. However be sure to sit in the front benches. If you are in a conference you can do the same with a voice recorder app from anywhere in the room. Rename the file with the date, class and topic name for easy referral.

Not only will this serve you to find important details for your assignments later, but it will also help you as a last minute study a few days before exams. All you have to do is put on your earphones and listen to the file you need. Quick revision can be done if you play the files at 1.3 or 1.4x the normal speed. Faster than normal but slow enough to comprehend. Same goes for conferences.

(AW- Anil)