Perfect balance is unachievable. Rotating machines vibrate. The only time when no vibration is perceptible is when the machines are stopped, so it is impractical to expect to find a non-vibrating machine when in operation. Balancing standards are formally defined for shop balancing, but in field balancing we have no field balancing standards, only industry guidelines. The purpose of this article is to clarify some of those guidelines for field balancing.