I just noticed that Grapher fails to evaluate a function at a constant. In the image, the graph of y = c should of course be a horizontal line. Is there a way to fix or work around it? This seems like such a fundamental bug that I can't understand why I haven't run into it before.
I suppose this might be considered off-topic because it's more about software than about math, but someone at apple.stackexchange.com suggested I try here.
One way to do this is to write an equation for $y$ in terms of a parameter, say $a$: $$y = a^3 - 3a + 5, \quad a = 1$$ is what you would enter as an equation (so it has a check box to the left rather than a green equals sign). This will plot a horizontal line $y = 3$. Then enter in the same equation but using the variable name $x$: $$y = x^3 - 3x + 5$$ with no other conditions, which will plot the curve itself for varying values of $x$. Grapher is a nifty program and you can do lots of fun things with it, but it's not the ideal tool to use for function evaluation.