# Some Important Points

• A measurement of a physical quantity is said to be accurate if the systematic error in its measurement is relatively very low. On the other hand, the measurement of a physical quantity is said to be precise if the random error is small.
• Errors are always additive in nature.
• For greater accuracy, the quantity with higher power should have least error.
• Absolute error is not dimensionless quantity.
• Relative error is dimensionless quantity.
• Least count

• Least count of vernier callipers

â‡’ Least count of vernier callipers

= 1 MSD Â­â€“ 1 VSD

where MSD = Main scale division

VSD = Vernier scale division
• Least count of screw guaze

• Smaller the least count, higher is the accuracy of measurement.
• Larger the number of significant figures after the decimal in a measurement, higher is the accuracy of measurement.
• Significant figures do not change if we measure a physical quantity in different units.
• When we add or subtract two measured quantities, the absolute error in the final result is equal to the sum of the absolute errors in the measured quantities.
• When we multiply or divide two measured quantities, the relative error in the final result is equal to the sum of the relative errors in the measured quantities.