Year 12s: what will be the first way you research your future options? >>

Boiling temperature in a distillation

We were given a mixture of two volatile substances (pentane C₅H₁₂ and cyclohexane C₆H₁₂) of unknown ratio and volume, and we were asked to do a fractional distillation and to record the boiling point of both liquids (to identify the substances with their refraction index, density, viscosity and boiling point).

We were asked to measure the temperature of the gas in the fractionating column at each mL of distilled liquid.
The heater was set at 50% until the temperature dropped (meaning there was "no more" pentane) and then was set to 100% to boil the remaining cyclohexane.
Graphically, we were told this would yield two constant temperature levels which would be our boiling points.
However, we got the attached graph (might be poorly translated from French).

Given that we got distilled substance at 38.2 degrees Celsius, would that correspond to the boiling point of the pentane (in theory, it is about 36,0 degrees Celsius at 760 mmHg)?
Should we rather consider the average of the temperatures on the interval before we set the heater to 100% (being 40,0 degrees Celsius)?