File:Vernier scale zero error +0.10.gif

English: This animation shows how to read calipers when there is a "zero error". In most cases, it is ideal that a caliper read 0.00 mm when the jaws are closed but the caliper in the animation shows a reading of +0.10 mm. This is the caliper's zero error, which in general may be zero or negative too. Since all measurements with these calipers would then overestimate lengths by +0.10 mm (i.e., a systematic error), the zero error must be subtracted from all length measurements. The formula for a proper reading of a caliper is "(actual reading) = (main scale) + (vernier scale) - (zero error)". In the animation, the main scale reading is 19.00 mm and the vernier scale reading is 0.54 mm, so the actual reading is 19.00 + 0.54 - (-0.10) = 19.44 mm. The error of the instrument is the width of the smallest sub-interval which is 0.02 mm in this case. The complete reading can be expressed as 19.44 mm ± 0.02 mm.