Pretty sure it couldn't have worked by measuring the heat given off by the bread as:
(a) That would have been overwhelmed by the heat given off by the elements,
and
(b) Toast turns brown as a result of heat over time, so simply heating the bread a given temperature would not be enough - you need to heat it to a temperature for a certain amount of time (which will vary according to the type of bread, the moisture in it, etc, etc.)



