Description: Measuring the absolute pressure of the enviroment using a digital barometer such as this has some interesting applications. By converting the pressure measured into altitude, you have a reliable sensor for determining the height of your robot, plane . Using a sensor as capable as the BMP180 you can achieve accurary of 1m, with noise of only 17cm in ultra high resolution noise. The device will operate at only 0.3uA meaning low current draw for battery powered applications. The BMP180 comes fully calibrated and ready to use. As the device operates over I2C we've added optional I2C pull ups that can be enabled using the PU (pull up) jumper on the board for your convenience and ease during breadboarding. Using I2C, the device provides pressure and temperature as 16bit values, which are used along with calibration data within the device are used to provide a temperature compensated altitude calculation.  BMP180 Features: 1.8V to 3.6V Supply Voltage Low power consumption - 0.5uA at 1Hz I2C interface Max I2C Speed: 3.5Mhz Very low noise - up to 0.02hPa (17cm) Full calibrated Pressure Range: 300hPa to 1100hPa (+9000m to -500m) Weight: 1.18g Size: 21mm x 18mm  BMP280 has stepped up their game with their new BMP280 sensor, an environmental sensor with temperature, barometric pressure that is the next generation upgrade to the BMP085/BMP180/BMP183. This sensor is great for all sorts of weather sensing and can even be used in both I2C and SPI This precision sensor is the best low-cost, precision sensing solution for measuring barometric pressure with ±1 hPa absolute accuracy, and temperature with ±1.0°C accuracy. Because pressure changes with altitude, and the pressure measurements are so good, you can also use it as an altimeter with ±1 meter accuracy Typical application: Enhancement of GPS navigation e.g.time-to-first-fix improvement,dead-reckoning,slope detection Indoor navigation(floor detection,elevator detection) Outdoor navigation,leisure and sports applications Weather forecast Health care application(e.g. sirometry) Vertical velocity indication(e.g. risk/sink speed) Target devices Handsets such as mobile phones ,table PCs,GPS devices Navigation systems Portable health caredevices Home weather stations Flying toys Watches PCB size:(L*W)1.52* 1.20cm/0.60"*0.47"