There are two parts to your problem: (1) The numeric palette has a "horizontal progress bar indicator" Use this on the front panel (..or the one from the dialog controls).
(2) You need to write to it at regular intervals in your code. For example, if your main computing loop does 1000 iterations, just place the terminal in the loop and wire N to it. Make the scale go from 0...1000. There are many other ways to do this and you can get arbitrarily complex if the code is complicated. You might need to write to it from different parts of the code using e.g. locals.
