Metre Scale

NCERT Class 11, Chapter 2 emphasises that the least count of an instrument sets the smallest quantity it can measure, and for a standard metre scale graduated in millimetres the least count equals the smallest marked division, which is 1 mm. Although a skilled observer may estimate a fraction of a division by eye, the smallest value that can be read directly and reliably from the markings is one millimetre. The value 0.1 mm is wrong because that resolution requires a vernier calipers, not the unaided markings of a metre scale. The value 1 cm is wrong because it quotes the coarse centimetre gradation, ignoring the finer millimetre subdivisions actually present. The value 0.5 mm is wrong because half-millimetre marks are not standard on an ordinary metre scale, so it cannot be read directly. A consistency check confirms that the direct reading limit matches the finest engraved division, which for a millimetre-graduated metre scale is exactly 1 mm, and finer measurements demand a higher-resolution instrument.