Sensitive Altimeter. This Android application measures air pressure using internal barometric sensor in the portable device and displays it on a three-pointer altitude indicator similar to the altimeter gauge in aircraft. Digital indication is also available.
It can take a long time. Some employers move very quickly, and others move very slowly. People have been hired three hours or three months (or more) after interviewing. Moreover, hiring nearly always takes longer than employers expect it will; you should generally double or triple whatever timeline they give you.
Arriving 15 to 20 minutes before your scheduled interview is acceptable. Any more than that, and you may be sending the wrong message. Plus if you arrive too early, the staff may feel like they need to entertain you or continue offering you coffee, etc. They're trying to make a good impression too.