You have that the tolerance for the shelflength is of ± 0.8 cm. The shelflength should be of 105 cm. If you take into account the tolerance, the maximum and minum allowable shelflength will be:
maximum allowable shelflength = 105 cm + 0.8 cm = 105.8 cm
minimum allowable shelflength = 105 cm - 0.8 cm = 104.2 cm