This is a breakout board for the Bosch BMP180 high-precision, low-power digital barometer. The BMP180 offers a pressure measuring range of 300 to 1100 hPa with an accuracy down to 0.02 hPa in advanced resolution mode. It's based on piezo-resistive technology for high accuracy, ruggedness and long term stability. These come factory-calibrated, with the calibration coefficients already stored in ROM. What makes this sensor great is that it is nearly identical to its former rev, the BMP085!
This breadboard-friendly board breaks out every pin to a 6-pin 0.1" pitch header. VCC can be from 1.8V to 3.6V and is 5V tolerant; we typically run it on a clean, regulated 3.3V supply. The analogue and digital supplies (VDDD and VDDA) are tied to a single header pin, but are separately decoupled. It connects to a microcontroller via I²C bus (also known as TWI, or on the Arduino, the "Wire" library).