A calculation consists of one or more measures and may include any number of dimensions. One calculation typically corresponds to one presentation, although it is possible to have multiple presentations for one calculation. A dimension is the entity around which the results are grouped in a table or a graph. A dimension can have any number of values associated with it. For example, the dimension Year could have a number of measures associtated with it, including Number of Hits, Number of Users, and Number of Referring Organizations.
Measures are the values that are actually counted in a calculation.
A measure can have only one value associated with it. For example, the measure Number of Visits represents a single value. A presentation is a table or graph. You can have more than one presentation per calculation if you want to display the data in different formats. You have a number of options for modifying the formatting of a presentation.