I'm trying to figure out what a callback procedure is exactly and why it is useful. It looks to me to be something like this:

Total = GetTotal (x as integer, y as integer, FigureTax) as Single
X + Y = Total
End Function

Where GetTotal is just a general procedure and AFTER the GetTotal general procedure executes it will automatically run the FigureTax procedure. So you get the total of X+Y figured by GetTotal and then the FigureTax applies a tax formula to create the final value for Total.

Is this accurate?