The guidelines for most daycares is a temperature of 101 - so I've always figured that your temperature means little until it's at least 101 for a period of time (like a day).

An old medical book I have states, "Temperature varies with time of day and other factors, so don't worry about minor changes." It also says that for "most people" normal temps are from 97.6 to 99.6 - this is for oral readings. The book I have is too old for digital.