<P> While computers and digital clocks display `` 12 : 00 a.m. '' and `` 12 : 00 p.m. '' , those notations provide no clear and unambiguous way to distinguish between midnight and noon . Strictly speaking , it is actually incorrect to use `` a.m. '' and `` p.m. '' when referring to noon or midnight ( 12 : 00 ) . The abbreviation a.m. stands for ante meridiem or before noon and p.m. stands for post meridiem or after noon . Since noon is neither after noon nor before noon , and midnight can equally be twelve hours before and after noon , neither abbreviation is correct ( although the length of the error is determined by the smallest unit of time -- 12 : 00 : 01 p.m. would be the correct notation for `` 1 second after noon '' ) . </P>
<P> While computers and digital clocks display `` 12 : 00 a.m. '' and `` 12 : 00 p.m. '' , those notations provide no clear and unambiguous way to distinguish between midnight and noon . Strictly speaking , it is actually incorrect to use `` a.m. '' and `` p.m. '' when referring to noon or midnight ( 12 : 00 ) . The abbreviation a.m. stands for ante meridiem or before noon and p.m. stands for post meridiem or after noon . Since noon is neither after noon nor before noon , and midnight can equally be twelve hours before and after noon , neither abbreviation is correct ( although the length of the error is determined by the smallest unit of time -- 12 : 00 : 01 p.m. would be the correct notation for `` 1 second after noon '' ) . </P>
when does the time change from am to pm
when does the time change from am to pm
noon
noon