AT mileage markers

Is it safe to assume that the mileages listed on the ATC website are probably the most accurate and up-to date? It seems like every website I go on, the "miles from Springer" vary for each shelter, peak and road crossing by anywhere from 0.1 miles to even 2-3 miles. I would love to use an all-inclusive reference for planning out some longer section hikes. Any advice?

Reminds me of a sign in the Colorado Rockies. Per the Forest Service, Three Island Lake was five miles away. However, each year the sign was altered by exhausted hikers (it is a steep trail, and the air is a bit thin up there). The last time I saw that sign, Three Island Lake was "1,115 miles BY AIR."

Actually, having ridden the trail on a horse numerous times and having hiked it twice, I thought that 5 miles was pretty close. The sign is no longer there, the trailhead having been moved two miles closer to the lake some time between 1958 and 1988.

While you'd think modern methods would be more accurate, I keep seeing differing mileages on trails measured by GPS (depends on who is measuring, it seems). Those GPS distances are almost always shorter than those trails measured the old-fashioned way with an odometer on a wheel (usually done only for short, popular trails). Of course most trail signs seem to use map mileages. Modern guidebooks also differ, sometimes considerably, when different authors describe the same trail.

Example: Our local hiking forum, oregonhikers.org, has GPS mileages in its Field Guide. The popular hiking guides to the same trail often have different numbers, usually greater. Trip reports where the hikers have taken a GPS and measured the mileage themselves are often different yet.

I try not to get too hung up on exact mileages. I don't think they exist!

Thanks OM. I only ask because being off by 1 or 2 miles can be the difference between a late day summit after a long hike before you reach your intended destination and starting out the next morning on somewhat fresher legs and heading uphill. As long as I can trust where things are in relation to each other, I'm less concerned...

The mileages for any long trail change all the time; often minor changes, sometimes significant ones, such as some major PCT re-routing in SoCal. This can come about based on physical trail changes on the ground or from more accurate (?) measurements.

If you want an up-to-date measurement in a way that's useful for trip planning, the latest guidebooks will likely have the latest official mileage. One option is to join ALDHA for $10 and from that have access to the pdf version of their guide, the 'Companion'. http://www.aldha.org/companion.html You can look at this at home on a larger screen, and/or carry it with you on a smartphone. I did the latter on my AT trips, as a backup to my main guide ---I liked using AWOL's "A.T. Guide". You can get this for $16, or $9 as a pdf download.
http://www.shop.theatguide.com/Books_c3.htm

But without studying the issue, I would assume that mileages given on the ATC website are good.