Date: Dec 8, 2012 1:28 AM
Author: Richard Fateman
Subject: when is y=x+a not a straight line?

Try this

a=0``-0.5
ListPlot[Table[{x, a + x}, {x, -10, 10}], Joined -> {True}]

This is probably not a surprise to some people.

If you think the value for "a" could never happen, try this:

a=N[1,20]
Do[a=2*a-a,{43}]

Compare to Plot[x+a,{x,-1,10}]
which shows that Plot evaluates its first argument in an manner
inconsistent with Table's method.

Cheers.
RJF