These gauges have two scales for fine adjusting—a main scale and a sliding vernier scale. The vernier scale takes the space between graduation marks on the main scale and divides them into smaller increments for an accurate depth reading. Use the adjustment screw on the vernier scale for fine tuning. Designed for durability, these analog gauges are good for measuring the depth of small holes and slots in machine shops where they’ll get frequent use. They are often used to set the cutting depth for milling tools and counterbores.