After upgrading to PA 6.5.4, there is now no variation in the Performance Baseline. It is a constant range through all of the historical data.
The baseline comparison is drawn on a daily basis and is compared against the same day, last week. This allows daily trends to be monitored and readings from quiet days, like weekends, do not affect the statistics.
It may take two full working weeks for the Baseline to begin correcting itself as at least two works days (eg. Mondays) are required for comparison.
Allow two full weeks after installation for the PA Agent to bed in and for the Baseline metrics to begin reflecting the daily workload.
Please see the Performance Analysis Help section; type in 'Performance Baseline' in Index search for more information.