The given diagram shows two different scales on a Vernier callipers.The reading on the main scale is

Explanation

To determine the reading on the main scale of the Vernier caliper shown in the diagram, we need to observe the position of the zero mark of the Vernier scale relative to the main scale.The main scale is marked in centimeters (cm) and millimeters (mm). Each major division represents 1 cm, and the smaller divisions represent 1 mm (or 0.1 cm).Upon close inspection of the image: * The zero mark of the Vernier scale is located past the 6 cm mark. * It has also passed the 6.1 cm, 6.2 cm, 6.3 cm, and 6.4 cm marks. * However, the zero mark has not yet reached the 6.5 cm mark.In standard Vernier caliper operation, the main scale reading is the value on the main scale immediately to the left of the zero mark of the Vernier scale. Based on this, the main scale reading would be 6.4 cm.