Each discrete tick on the X axis represents a week, where the Y value represents the sum of expenses in that week. As per fpos custom, the Y value is negative as the graph only considers expenses. The week label (X) should be ignored, it's enough to know that the last completed week is the right-most data-point (The X axis labelling could do with some improvement). A line of best fit is provided to roughly show whether weekly spending is increasing or decreasing over what is approximately a 52 week period (there may be less data points if the most recent transaction date is not in the last week of a month).