How to know whether Bishop or Knight is stronger

Sort:
Avatar of ABC_of_EVERYTHING

Here again I exchange my bishop. Look at the engine bar how it dropped. 

It always happen only with bishop. Look here again I exchange bishop,



Avatar of ABC_of_EVERYTHING

Maybe it's because of the 3 points for both knight and bishop. 

Avatar of ABC_of_EVERYTHING

So what's the purpose of bishop in chess game. Don't say it only needed to control diagonal.