Ground and graduated main vialThe base of the level features an involute groove running the length of the base, which provides a reliable seat for round workCross test vialVial is adjustable to a positive setting and is housed in a satin finished brass tube with a friction-fit closing cover to prevent breakageMain level vial has graduations that are approximately 80-90 seconds or 0.005" per foot (0.42 mm per metre)