<html><head><style type='text/css'>p { margin: 0; }</style></head><body><div style='font-family: arial,helvetica,sans-serif; font-size: 12pt; color: #000000'>Derek,<div> I'm pretty sure Ron realized that--that's why he mentioned getting it from online sources for his locality. The problem was they all reported different values.</div><div><br></div><div>Separately,</div><div><br></div><div> A family member gave me a fancy weather station / atomic clock (well, it supposedly reads the atomic clock radio signal) with an outdoor remote unit this Christmas. It tells the indoor/outdoor temperature, pressure, and other stuff. Testing it out, I place the remote unit right next to the indoor unit and they consistently reported values 10 points off! It also never read the clock signal. Oh well, so much for technology.<br><br>Scott</div><div><br><hr id="zwchr"><div style="color:#000;font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt;"><b>From: </b>"Derek Atkins" <warlord@MIT.EDU><br><b>To: </b>"Atlanta Linux Enthusiasts" <ale@ale.org><br><b>Sent: </b>Tuesday, February 26, 2013 11:17:53 AM<br><b>Subject: </b>Re: [ale] WAY [OT] but geeky - how do I calibrate GPS barometric altimeter<br><br>Ron,<br><br>...</div><div style="color:#000;font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt;"><br>The issue is that the barometric pressure is constantly changing.<br>Pilots use barometric altimeters, and the rule is that they need to<br>reset them every 100 miles or every hour. An airport will report the<br>current altimeter setting every hour, but some automated systems will<br>report it every minute, and yes, it can change rapidly if you have<br>strong storm systems.<br><br>Basically, this is a long-winded way of saying that you need to be<br>constantly resetting altimeters. When they are set properly they are<br>very accurate. However they need to be reset frequently to remain<br>accurate.<br><br>One tip: the barometric pressure doesn't usually change significantly<br>over short distances. Most of the local airports will have the same<br>setting, so you could theoretically just dial the weather at, say,<br>Kennesaw (770-425-3406), to get a local altimeter setting that should be<br>"close enough" for you. Worst case you'll be maybe +/-50 feet off, but<br>is that really too much error for your use-case?<br><br>-derek<br><br>-- <br> Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory<br> Member, MIT Student Information Processing Board (SIPB)<br> URL: http://web.mit.edu/warlord/ PP-ASEL-IA N1NWH<br> warlord@MIT.EDU PGP key available<br>_______________________________________________<br>Ale mailing list<br>Ale@ale.org<br>http://mail.ale.org/mailman/listinfo/ale<br>See JOBS, ANNOUNCE and SCHOOLS lists at<br>http://mail.ale.org/mailman/listinfo<br></div><br></div></div></body></html>