üle takistuse kulgeva mõõdulindiga mõõdetud mahuti pinnal asuva kahe punkti näiva vahekauguse ja üleastme mõõdetud tegeliku kaarepikkuse (üleastme konstandi) vahe, difference between the apparent distance between two points on a tank shell as measured by a strapping tape passing over an obstruction and the true arc distance as measured by a step-over, i.e. the step-over constant