vlad2005:
I don't know!But here's my dilemma. Supposing that ISR routine can't capture each pulse from both sensors witch is very probable.
This is very improbable. The reason for using interrupts is to make sure you don't miss any when they are occurring at high speed (hundreds or thousands per second.) If the analog circuitry is OK - no glitches from RFI interference - then the count should be very reliable.
If there are glitches, then there's no reason to say that the number of glitches will be the same going forwards or in reverse. So you can't rely on that.