Vernier Calipers
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flagWhat you'll discover
- arrow_forwardState and compute the least count of a vernier calipers
- arrow_forwardTake a reading by combining main scale and vernier coincidence
- arrow_forwardIdentify positive and negative zero error and apply the correction
- arrow_forwardMeasure diameter, length and internal depth of regular objects
- arrow_forwardList precautions that reduce errors with vernier instruments
Why a vernier beats a plain ruler
A metre ruler can read to 1 mm at best — your eye simply cannot split a millimetre reliably. The vernier calipers adds a small sliding scale whose 10 divisions span only 9 main-scale millimetres. Because each vernier division is 0.9 mm, exactly one vernier line will coincide with a main-scale line, and which one it is tells you the fraction of a millimetre.
Least count = 1 MSD − 1 VSD = 1 mm − 0.9 mm = 0.1 mm = 0.01 cm. Total reading = main scale reading (the mark just before the vernier zero) + coincident division × least count. With this trick a Rs 300 instrument measures to a hundredth of a centimetre.
Procedure and zero error
Close the jaws gently on the object — sphere or cylinder between the outside jaws, a beaker depth with the depth rod or inside jaws. Note the main scale reading just left of the vernier zero, then scan the vernier for the line that exactly coincides with a main-scale line. Repeat at different orientations of a sphere and average, because real spheres are never perfectly round.
Before measuring, close the jaws fully with nothing inside. If the vernier zero sits right of the main zero the error is positive and must be subtracted from every reading; if it sits left, the error is negative and is added. Corrected reading = observed reading − zero error (with its sign). NEB examiners love asking this correction rule.
Sources of error and precautions
The biggest error is over-tightening: squeeze a soft object and you measure the squashed size, not the true one. Hold the calipers square to the object — a tilted jaw reads long. Parallax while spotting the coincident line is another classic mistake; view the scales perpendicularly.
Precautions to write in your report: check and record zero error first, grip gently without pressure, take at least three readings at different places and average, and keep your eye directly above the coincidence. Mentioning instrument wear (loose jaws on an old calipers) earns extra credit as a source of systematic error.