I usually use markers, sometimes it's a 100 meters sign o something similar like when something appears o disappears from the screen, but you also have to use your own judgement in every corner because of the several factors that involve braking, brake presure, dirt in the tyres, moving cars around, racing line, speed, every thing makes part of a whole when braking for entering to a corner. I like to belive that braking points are not really important as how you brake.