1.3.1　Basic concept of significant figures

Significant figures are closely related to that of the measurement error.Since measurement error is inevitable,both observations and measurements are approximations.Significant figures are to indicate how reliable the approximations are.The measured values are usually estimated to a few tenths of the minimum scale of the measuring apparatus in one measurement.Thus,error exists in the last digit of a measured value,which is called doubtful figures.The other figures on top of the doubtful figures are accurate,which are called reliable figures,say for reliable figures,together with the last digit of relevant doubtful figures,constitute the significant figures.(https://www.daowen.com)