What you should know - In 150 words or less:
At the end of each day, the USGA centralized computation system compares the actual scores made at each course to the expected scores of the players who made them. If the scores were significantly higher or lower than expected, an adjustment is automatically applied to everyone who played the course on the day.
The range of the PCC adjustment is -1 to +3, with a negative (-) adjustment meaning the course played easier than expected, and a positive (+) adjustment meaning the course played more difficult. On most days, the PCC will be zero (0). If a PCC is applied following one of your rounds, it will be clearly identified within your scoring record.
WHY EVERY SCORE MATTERS:
At least 8 scores must be posted before midnight (local time) in order for the calculation to take place - so it's important for all of us as players to post our scores on the day of play.