A student investigated how the number of layers of bubble wrap affects the rate of thermal energy transfer from a beaker of hot water. The student's results are shown in the graph below. 
a.[6]
Describe a method the student could have used to obtain the results shown in the graph.
b.[2]
The student considered using a temperature probe connected to a datalogger instead of a digital thermometer. Both instruments display readings to one decimal place (e.g., 72.4∘C72.4^\circ\text{C}72.4∘C). The datalogger can record 20 readings per second. Explain why it was not necessary to use a temperature probe and datalogger in this investigation.