The parameter P21 (arccot(-0.1)) must be 1,670 and not -1,47.
This is a very old message, and I have a vague sense that at one point this was answered, and I'm very certain that Roland's simulator and other simulators now agree on the point. It may be related to the time when all tracker item comments were accidentally deleted--we restored many of them, but this might have been lost.
However, for the sake of posterity, this is what was decided.
In general, there seems to be disagreement about this. According to https://mathway.com/ the correct answer is -1.47. According to http://www.thinkcalculator.com/trigonometry/inverse-trig.php, the answer is 1.67. I think the difference is summarized at http://www.intmath.com/blog/mathematics/which-is-the-correct-graph-of-arccot-x-6009, and the fact that the difference between those two values is basically 'pi' seems suspicious. For the sake of consistency (which is the point of the test suite), let's stick with -1.47, since that's what other interpreters have had to use.
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