Porsche Boxster Owner's Manual page 151

The tire pressure to be corrected (refill pressure)
is indicated on the displayed wheel.
Example: If " –1.5 psi (–0.1 bar)" is displayed,
1.5 psi (0.1 bar) must be added to this tire.
Note
The tire pressure menu can only be called up when
the vehicle is stationary.
Calling up the "Info pressure" display
f Push operating lever forward in order to switch
on the selection field.
f Select "TPM" with the operating lever.
f Push operating lever forward.
The display changes to the tire pressure menu.
f Select "Info pressure" with the operating lever.
f Push operating lever forward.
Note
After the ignition is switched on, it can take up to
approx. 1 minute before all tire pressures are
displayed. Dashes ("-.-") appear instead of the tire
pressures.
Tire type info in Tire pressure menu
Information about the currently set tires:
– Tire type: Summer tires, winter tires
– Tire size: 17, 18, 19 inch
"Info tires" shows the current tire settings.
Calling up the "Info tires" display
f Push operating lever forward in order to switch
on the selection field.
f Select "TPM" with the operating lever.
f Push operating lever forward.
The display changes to the tire pressure menu.
f Select "Info tires" with the operating lever.
f Push operating lever forward.
Tire selection in the "Set" menu
f Push operating lever forward in order to switch
on the selection field.
f Select "TPM" with the operating lever.
Instruments, On-Board Computer, Warnings
149