[civility]

Call it a contrivance if you want, my point was just that you can get very surprising results even for "real life" sized numbers.

Not sure why you changed it from "1.0 % 0.2" to "0.1 % 0.2". The error on the one I showed was near 0.2, not 1e-17. Did I miss your point?

[tomxor]

I mistakenly used 0.1 instead of 1.0 but the _numerical_ error is still x10-17, the modulo is further introducing a discontinuity that creates sensitivity to that tiny numerical error, whether that is a problem depends on what you are doing with the result... 0.19999999999999996 is very close to 0 as far as modulo is concerned.

I'm not arguing against you just clarifying the difference between propagation of error into significant numerical error through something like compounding; and being sensitive to very tiny errors by to depending on discontinuities such as those introduced by modulo.