TeamDino5280 wrote:If you are using USGS 7.5 minute quads the accuracy for vertical rise is 90% within half the contour interval. I think these have 40' contour lines which means that the change in elevation between contour lines should be 90% accurate within 20'. Now I think that you would need to take into account a 20' (+- 10%) error margin in the calculation.... total speculation on that one.
I think you are on to something here. Most slopes I am thinking of hiking, that warrant checking, are in the mid-twenty to mid-thirty degree range. And now that I think about it, it seems to be closer to 2 degrees off when measuring in the low to mid twenties...and closer to 3 degrees off when measuring in the upper twenties/low thirties. And just last week I measured a slope off the map at 38 degrees and the field check came in around 42 degrees. At the time I just wrote it off as a micro feature in the terrain. But now I see a pattern. Upper thirties being closer to a 4 degree inaccuracy makes sense. From now on I will use a 10 percent adjustment instead of a 2 to 3 degree adjustment. Thanks TeamDino!
Also, just wanted to mention a plus for an old school compass/inclinometer. The mirror. Ever get some debris in your eye when bushwhacking? And of course the possiblity of needing a signal mirror if lost/injured.