I’m gathering data online for an industrial product whose various manufacturers document performance with graphs having logarithmic axes. I’m then digitizing the graphed curves and doing further analysis with the numbers. But I discovered something that seems REALLY WEIRD. The graph axes in 8 out of 8 cases have huge inaccuracies. That is, the tick marks are very far out of place. They’ll be several percent off, even tens of pixels.
On a logarithmic axis, if I import the graph to a graphics editor such as Microsoft Paint and copy a little region through which the tick marks for 10 and 20 pass, the distance between those marks represents a factor of two. If I then paste that elsewhere in the image, like over the lines for 3 and 6 or the lines for 50 and 100, the tick marks and the lines should match because there is a factor of two for these lines also. Yet they don’t.
For one example I copied the 1 and 2 tick marks to place the 1 over a 50, and I found that the 2 was over the high 80s and didn’t even reach to the 90, let alone land on the 100.
I took all 8 graphs I downloaded from these manufacturer’s web sites and experimented on both horizontal and vertical axes, and did not find a single one that did not have errors of a few percent or more.
It is obvious that these are separate manufacturers graphing separate data sets, so this isn’t a case of one bad graph getting copied everywhere else. And, I don’t have independent versions of the curves themselves to compare (that’s why I’m digitizing graphs in the first place). At this point all I can tell is that every logged axis I grab online has enormous errors.
Is there some common computer oddity that could cause everybody who tries to publish their graphics to suffer distortions?
I remember, I think this was in the Win32API but am sure it was someplace with broad application, there’s a base function called DrawOval that draws an ellipse instead of an oval. And we all remember the Intel division bug. I’m wondering if there is some deep error someplace that propagates to all log axes on the web.