Most materials expand and contract with temperature change, and this effects taped distances. If a tape has stretched due to heat it will read shorter than it would at its normal (or standard) temperature. The corrected length is computed as follows:

L = 1 + 1.c.Dt

For example, if;

t = 20°C (usual) t = 37°C (hot!)
l = 79.984
c = 1.15 x 10^-5m/°C

then:

L = 79.984 + 79.984 x 1.15 x 10^-5 x 17 = 80.000m

So, if a distance of 79.984m was measured at this temperature, the actual distance would have been 80.000m. Conversely, if it was needed to lay out a line of 80.000m then a tape distance of 79.984 would be used.