Vernier caliper simulator

1. Close the jaws on the object and read the main scale at the vernier's zero mark: the last whole millimetre mark to its left.
2. Find the vernier division that lines up exactly with any mark on the main scale. Each division is worth 0.1 mm.
3. Add the two readings, then correct for any zero error.

For example, if the vernier's zero is just past 23 mm and the 7th division is the one that lines up, the reading is 23 + 0.7 = 23.7 mm.

The vernier scale has 10 divisions that together span 9 mm, so each is 0.9 mm long: 0.1 mm shorter than a main scale division. If the vernier's zero is 0.3 mm past a main scale mark, the third division is the one that lines up, because each earlier division has gained 0.1 mm on the main scale.

Close the jaws with nothing between them. If the reading isn't 0.0 mm, that's the zero error: subtract it from every reading (add its size if it's negative). The uncertainty in a vernier caliper reading is usually taken as the smallest division the instrument reads: ±0.1 mm for the 0.1 mm vernier here. Many school calipers are finer, reading to 0.05 mm or 0.02 mm (with 20 or 50 vernier divisions), and their uncertainty is correspondingly smaller. This simulator uses the 0.1 mm kind.

• Reading the main scale at the wrong mark: it's to the left of the vernier's zero, not the nearest one.
• Choosing a vernier division that is nearly, but not exactly, in line. Look for the best match.
• Reading the vernier division number as millimetres instead of tenths of a millimetre.
• Applying the zero error the wrong way round.