Explain the need for a reference atom for Atomic mass? give some information about to reference atoms. please don't copy from Goógle​

The independent variable is the type of music.the dependent variable is the pulse rate.the intervening variable is the age of the subject.if the mother does not like rock, her pulse is likely to not increase.the same might be true for the sister.the friend may like rap and gets excited.to establish cause/effect relationship, all of the subjects must be consistent.hope i .

Ithink ahopefully im correct