I didn't bother with 1 nm measurements. To fly better than about plus/minus 3 degrees over 60 nm is doing pretty good. Also, without decent ground features to identify the 1 in 60 technique is hard to apply. Here's a track I flew on a wet and windy day. Dodging rain showers made things interesting. The GPS was just logging my track, no display available.
Maybe there is no link to the graph, the dude who posted it may have created it himself. I'd like to know what he used as Excel is crap. I use Python for stuff like that.