# Why does this linkage calculate log?

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

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.

• 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. Jan 3 '20 at 5:26
• @joojaa Both scales are linear. Jan 3 '20 at 6:37
• @GregBell but not the same linear length... is the ratio of lengths about 2.7? Jan 3 '20 at 6:45
• @SolarMike in this case 3.5 Jan 3 '20 at 7:10
• It's not even a good approximation. Log 2 = 0.3010 but the diagram shows about 0.27. Jan 3 '20 at 10:26