The Historical Maximum Speeds are high-watermark values of the maximum speedtest results for every agent.
Each time a speedtest is executed with an agent, the historical maximum download and the historical maximum upload are compared with the results. If the results are higher, they update the historical maximum value.
The Historical Maximum Speeds can be erased by editing the Agent Advanced Parameters. This is useful if there is a change on the connection speed or the agent is moved to another location.