It can be seem like not a big problem, but to me, cause of this, it takes my few seconds when I use this serial data....
I'm using qmc5883 magnet sensor , I2c expander and mega board.
I'm sure the hardware doesn't have any problem.
But when I push serial monitor button, there are always show inverse ?mark.
Forexalmpe, say, I take 2 magnet sensor data
Now always like this but, frequently this problem is occur.
Sometime, not the inverse ?mark, other strange mark was shown.
this problem is only at the first line of serial.