When the required length of a calibration course was reduced in the late eighties, the instructions were pretty much as Mark has suggested: If the temperature is above 68 degrees F, don't adjust. If it's below 68, add length to the calibration course.
Usually a count on my bicycle works out to be about 9 cm. The constant for my tape is 0.0000093 per degree C, so for the adjustment to be more than half a count, the temperature has to be above 36 or below 4 degrees C. I seldom encounter the former, and try to avoid measuring in the latter as much as possible.