The phrase "last graph" refers to the final or endmost section of a graph or chart that displays information or data. It is the graph or chart that comes after any other graphs or charts that might be present. Full definition
On the very last graph (at the bottom), there is a «ringing» that is not seen on the other peaks. (wattsupwiththat.com)
Also, comma at start of last graph is not needed. (bmoreart.com)
This is due to an increase in the trade winds that push water westward across the tropical Pacific, while in the east cold water from the depths comes to the surface (see last graph here). (realclimate.org)