PH Calibration - Usage of Std Buffers (Dec/27/2006 )

Why do we use Buffers 4.0,7.0 and 10.0 for PH meter calibration..why not 0.0 ,7.0 and 14.0?

because the closer the standards, the more accurate the extrapolation between them. and most of the buffers used in biology, biochemistry and molecular biology are within the range of those standards.