Need help using yeast starter calculator

Hi, I know this has been a topic of many threads and I apologize for that. I've tried researching my questions but I will be brewing this coming weekend and I want to have my starter ready so please excuse me if the question has been discussed and answered previously.

When I use the Mr Malty calculator I see that the O.G is necessary to calculate the yeast starter, or at least it seems to be. What if you don't know the expected O.G. beforehand? My recipe doesn't list it. Should I just aim high, and have more than enough on hand? That way I could eyeball the amount of slurry I put in. But I don't even really know what "aiming high" means since this will only be my third batch and my first attempt at starter.

My last batch (ale) had an O.G. of 1.068, which calculates out to just under 3 quarts of starter. I could see where I could have had a gallon of starter on hand, decanted and then pitched 3/4 of the slurry. Would that be in the ballpark? If I do that can I save the unpitched portion in the refrigerator?

You might just stop on over to hopville.com's beer calculus and input your recipe, that will give you a good idea of a projected OG. Otherwise, I think a 2L starter is a good starting point for a lot of regular ales in the 1.06x range.

Awesome, just what I was looking for. Thanks!