Originally Posted by
a5in_the_sim
Were you on the ground in Amsterdam? Is this a serious question? FFS!
(my bold). Play nicely Draco...... It might be obvious to you but not the OP, hence why they are asking the question. (They might not be a pilot).
To answer the OP, this commonly happens at airports (near sea level elevation) if the atmospheric pressure has increased since the previous crew left the aircraft. The QNH they set before they landed now gives an altitude below sea level, and this is highlighted with the ‘NEG’ caption.