Nucleo F411RE How read encoder with 0.005mm step?

//example #1
var step = 0;
function encFun(){
var a = digitalRead(C6);
var b = digitalRead(C8);
//  print('a', a);
//  print('b', b);
   if (a == HIGH && b == LOW){
     step ++;
     print(step);
return;
}
else if (a == HIGH && b == HIGH){
       step --;
       print(step);
return;
}
}
setWatch(encFun, C6, true);