used to say that somethingincreasesorchangeswith everyminute,hour,day, etc. thatpasses:
Thedeathtollfrom thehurricanewasclimbingminutebyminute.
Thecredibilityof thecampaignhas deterioriated by theminute.
Thetemperatureherechangeshourbyhour.
Thedramaunfoldedminutebyminuteas rescuersattemptedto get to thetrappedhikers.
Thedepartmentis inchaos, and things arechangingdaybyday.
See alsobypreposition(MEASUREMENT)