Dig Control is Miller's name for adjusting the Open Circuit Voltage of the welding arc. The OCV is what determines how effective your welding arc is. Industrial welding machines have a high OCV. Hobby machines have a lower OCV.
This is why some rods don't work on hobby welding machines.
6010 is the best example, because it demands a high OCV to work right.
Increasing the DIG control actually lowers the OCV. This can help with rods like 6013 or 7014 by making the arc a bit softer and smoother.
7018 and 6010 like things a bit hotter.
It is one of those things I tell novice welders to just forget is there until their welding is consistent enough that they will be able to appreciate what it does.
Thanks for the response Ernie, but reason I'm confused is that OCV is the potential before an current is flowing. So the dig setting should only help you when you're starting the arc. Correct? But then, why do they call it "dig"? That term makes me think of getting better penetration during the weld.
It is a way of changing the amp-volt curve at lower arc voltages. Turning the dig control on (up) "flattens" the V-A curve at the lower end so that the amps increase a lot for any additional reduction in the arc voltage (i.e. as you are getting closer to sticking the rod).
You can see this in the V-A curves in the Miller operating manuals, for example, see page 16 (listed as page 16 but actually page 22 of the pdf file)
As quoted from Miller: The Syncrowave=92s adjustable DIG control lets you set the STICK arc force =96 which prevents electrode sticking while welding. The circuit is adaptive and is only active if the power source detects that the electrode is extremely close to the workpiece =96 and sticking is likely.
I am not very familiar with your inverter, but all drooping power sources are very responsive to operator technique and arc length. When working around experienced hands you will notice they do not spend much time adjusting their machines as they just vary their technique to compensate for changing work requirements. Modern software driven equipment provides a lot of capability to fine tune the output characteristics but adjustments (in arc volt /amp slope or anything else) are not intended to compensate for poor or inconsistent technique.
There was a similar question recently in the thread subject 'what is "did" control? my reply follows. It is more descriptive of slope adjustment using a dual dial generator but similar CC slope variation can be obtained by using different taps (or ranges) in transformer machines or by varying the slope with software in modern inverter (or generator) types. It is software control that enables modern generators (and transformers) to deliver CC (constant current / or drooping, for stick) or CC-HF (high frequency for TIG) or CV (constant voltage / for MIG) outputs.
What is the URL of the manual you downloaded?
Your questions raise the issue of semantics as these terms are often used in contradiction to expected usage and are also subject to varied definition and usage. Here is some information you may find helpful, note that I make no claim to be an electrical engineer.
Google 'drooping volt amp curve'
Google groups news: email@example.com...
CC welding generators have a drooping volt amp curve. This means that the voltage will vary between >60 volts OCV (open circuit volts) when not welding, ~ 40 volts when welding and