Question
Which of the following is the most precise device for measuring length :
(a) a vernier callipers with 20 divisions on the sliding scale
b) a screw gauge of pitch 1 mm and 100 divisions on the circular scale
(c) an optical instrument that can measure length to within a wavelength of light.
Solution
A device with minimum count is the most suitable to measure length.
a) 
b) 
Hence, it can be inferred that an optical instrument is the most suitable device to measure length.
