If you believe your client is showing incorrect PPD for a given slot, or just want to verify, you can use this Calculator from Linux Forge.
PPD is calculated as the median of the last 3 frames.
To Calculate for each device, you'll need:
The Project Number
Note: TPF is sometimes displayed incorrectly. Check the Logs in the [email protected] Client and find two to three consecutive "Completed" messages for the Slot you're evaluating. Calculate the time between them to discover your true TPF.