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The vernier callipers can read distance to an accuracy of 0.01 cm.
It has two scales: an ordinary one (fixed main scale), and a moveable vernier scale.
Here we use the lower scales, which are in centimetres. The upper scales are in inches.
Start at the beginning of the vernier (marked in read.) This is just past 1.2 cm.
Now look for where the marks on both scales line up (marked in blue).
Here they line up at the third mark on the vernier scale.
This gives us an extra decimal place. So the reading is 1.23
cm.