Reading the vernier caliper
Step 1: Find the hash mark on the ruler that perfectly aligns with or lies just to the millimeter measurement.
Step 2: Looking from left to right from the 0 hash mark, find the vernier hash mark on the vernier slide. This is the value in tenths of a millimeter (after the decimal point).
Step 3: Add the whole value together with the tenths value and you'll have the reading.
Step 3: How many millimeters does the vernier caliper indicate? 21 mm.