A drill rod assembly including inner and outer drill rods. The present invention relates to: a preservative efficacy-enhancing agent for antiseptic agents which includes an amphiphilic galactose derivative as an effective ingredient; a preservative efficacy-enhancing composition including 0. Particularly, a chuck is provided that includes a body, a retainer removeably attached to the body and a seal forming member. The difference between each adjacent resistance value in the set of resistance values may be selected to be greater than the greatest measurement error that may be incurred during measuring the actual resistance value.