Units and Measurements 
Systematic errors: It tends to be in one direction, either positive or negative.a. Instrumental errors b. Imperfection in experimental technique or procedure.c. Personal errors 
Random Errors 
Least count error 
Absolute ErrorThe magnitude of the difference between the true value of the quantityand the individual measurement value is called the absolute error of themeasurement. 
The arithmetic mean of all the absolute errors is taken as the final or mean absolute errorof the value of the physical quantity a. 𝛥amean=𝛥a1+𝛥a2+𝛥a3+ . . . +𝛥an n$\mathit{\Delta}{a}_{mean}=\frac{\mathit{\Delta}{a}_{1}+\mathit{\Delta}{a}_{2}+\mathit{\Delta}{a}_{3}+\phantom{\rule{0.22em}{0ex}}.\phantom{\rule{0.22em}{0ex}}.\phantom{\rule{0.22em}{0ex}}.\phantom{\rule{0.22em}{0ex}}+\mathit{\Delta}{a}_{n}\phantom{\rule{0.22em}{0ex}}}{n}$ 
Relative ErrorThe relative error is the ratio of the mean absolute error 𝛥amean$\mathit{\Delta}{a}_{mean}$ to the meanvalue amean$a}_{mean$ of the quantity measured.Relative Error=𝛥amean amean$Relative\phantom{\rule{0.22em}{0ex}}Error=\frac{\mathit{\Delta}{a}_{mean}}{{a}_{mean}}$ 
Percentage ErrorPercentage Error=𝛥amean amean×100 %$Percentage\phantom{\rule{0.22em}{0ex}}Error=\frac{\mathit{\Delta}{a}_{mean}}{{a}_{mean}}\times 100\phantom{\rule{0.22em}{0ex}}\%$ 
Rules for Arithmetic Operations with Significant Figures(1) In multiplication or division, the final result should retain as many significant figures as are there in the original number with the least significant figures. (2) In addition or subtraction, the final result should retain as many decimal places as are there in the number with the least decimal places. 
Rounding off the Uncertain Digits 

