Net plus-minus, aka unadjusted plus-minus, aka Roland Rating is invented by Roland Beech and measures the plus-minus statistics for a given player when the player is in the game relative to the plus-minus statistics when the player is NOT in the game. Net plus-minus combines offensive and defensive plus-minus.
For example, if a team scores 115 points (per 100 possessions) while a given player is on the court and 98 points (per 100 possessions) while he is off the court, his net offensive plus-minus is +17 (115-98=17).
If the team allows 110 points (per 100 possessions) while a given player is on the court and 105 points (per 100 possessions) while he is off the court, his net defensive plus-minus is +5 (110-105=+5).
So, net plus-minus for the given player is +17-(+5)=+12
TIP: It’s better to have a positive net offensive plus-minus and a negative net defensive plus-minus.