59. A spectrophotometer used for measuring CO concentration

[ppm (parts per million) by volume] is checked for accuracy by taking readings on a manufactured gas (called span gas)

in which the CO concentration is very precisely controlled at 70 ppm. If the readings suggest that the spectrophotometer is not working properly, it will have to be recalibrated.

Assume that if it is properly calibrated, measured concentration for span gas samples is normally distributed. On the basis of the six readings—85, 77, 82, 68, 72, and 69—is recalibration necessary? Carry out a test of the relevant hypotheses using the P-value approach with 
.05.