Sorry, I know this is an extremely late response but k = M / sqrt(L1 * L2) and so in fact 3.947 / sqrt(17.24 * 11.62) = 0.2788 as the tool reports.
I have moved development over to github, https://github.com/dmcmahill/wcalc and plan on using the bug tracker there. I also hope that I'll keep a bit more on top of them. My apologies for the extremely long delay.
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Shows entered data and result
Sorry, I know this is an extremely late response but k = M / sqrt(L1 * L2) and so in fact 3.947 / sqrt(17.24 * 11.62) = 0.2788 as the tool reports.
I have moved development over to github, https://github.com/dmcmahill/wcalc and plan on using the bug tracker there. I also hope that I'll keep a bit more on top of them. My apologies for the extremely long delay.
Marked as pending because I don't believe this is incorrect. Could you elaborate on why you think it should be ~0.05?