This is an Arduino library for the MPL115A2 pressure sensors. Pick one up at http://www.misenso.com/products/012/ To download. click the DOWNLOADS button in the top right corner, rename the uncompressed folder MPL115A2. Check that the MPL115A2 folder contains MPL115A2.cpp and MPL115A2.h Place the MPL115A2 library folder your /libraries/ folder. You may need to create the libraries subfolder if its your first library. Restart the IDE.