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From wikipedia, there's this animated GIF of a linkage.

Here's a frame from the animation:

Question: How does it calculate log? All I see there are trig functions and circles. log doesn't show up in geometric maths, does it?

My friend thinks it's just a (lucky) approximation.

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  • $\begingroup$ It does not need to do log functions since the scale can be calibrared to handle the difference. Anyway a fourbar function is really complex thing and can be made to do quite many things, luck has nothing to do with this. $\endgroup$
    – joojaa
    Jan 3 '20 at 5:26
  • $\begingroup$ @joojaa Both scales are linear. $\endgroup$
    – Greg Bell
    Jan 3 '20 at 6:37
  • $\begingroup$ @GregBell but not the same linear length... is the ratio of lengths about 2.7? $\endgroup$
    – Solar Mike
    Jan 3 '20 at 6:45
  • $\begingroup$ @SolarMike in this case 3.5 $\endgroup$
    – joojaa
    Jan 3 '20 at 7:10
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    $\begingroup$ It's not even a good approximation. Log 2 = 0.3010 but the diagram shows about 0.27. $\endgroup$
    – alephzero
    Jan 3 '20 at 10:26

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