The Pressure Plug is a little board for the BMP085 atmospheric / barometric pressure sensor:

An I2C bus running at 3.3V is used for I/O, with all the power and signal lines brought out to to both sides of the board to allow daisy-chaining with other I2C-conformant boards.
This sensor requires some calculations to arrive at the proper atmospheric pressure readings, these are included in the Ports library. Temperature measurements are also available, accurate to 0.1°C.
Configuration
There is nothing to configure. The BMP085 chip on this plug responds to I2C address 0x77.
The oversampling setting of the BMP085 sensor is described on page 10 of the datasheet:

Header Pinouts

Design Info
Dimensions: 21.1 x 24.1 mm
CadSoft EAGLE design files: jlpcb-065.pdf / jlpcb-065.sch / jlpcb-065.brd.
This board uses the conventions of a JeePlug and can be used with the ports on a JeeNode. It can also be used with other boards and MCU's, if you hook it up properly and adapt the interface code for it.
How to Get It
http://shop.jeelabs.com/products/pressure-plug
Related Weblog Posts
- 2009-11-12 - Meet the Pressure Plug
- 2010-05-27 - BMP085 in high-resolution mode
- 2010-06-05 - Switching from direct serial to wireless
- 2010-06-06 - Why use acknowledgements
- 2010-06-20 - Battery savings for the Pressure Plug