Calculate provides a powerful facility to convert data from its collected form to something that may be more relevant for data analysis. 


For example, when considering Boyle's law, it is the pressure that will vary with the inverse of the volume. So if you did a Snapshot experiment, using the prompt to collect the volume, the data isn't in the final desired format. 


Calculate allows the creation of a new variable (in this case 1/volume) to be generated and subsequently plotted.    


There are many calculation possibilities, these can allow for baseline offset and mathematical manipulation.