The `zero` value is the default threshold for values approaching 0.0.
Syntax:
set zero <expression>
show zero
`gnuplot` will not plot a point if its imaginary part is greater in magnitude than the `zero` threshold. This threshold is also used in various other parts of `gnuplot` as a (crude) numerical-error threshold. The default `zero` value is 1e-8. `zero` values larger than 1e-3 (the reciprocal of the number of pixels in a typical bitmap display) should probably be avoided, but it is not unreasonable to set `zero` to 0.0.