As much as possible, a pin should be set in an upright or "PLUMB" position. Plumb is at 90 degrees to a level or horizontal plane. A golf green pin should not be perpendicular to the green surface because a green surface is not usually level. If the pin is set at a 90 degree angle to what we would consider a "level line", then a golfer can look down the fairway and see how drastic or how little a green surface deviates from a level surface.