[intrasight]

I don't understand your "a general problem" statement. I would not consider it a problem to show correct results. Someone saving for retirement just wants to know the course-grained results. Having the chart split those results by the period that funds were invested would make for a very visually cluttered chart. But I agree that it would be interesting to some.

A few years back, I created a simulator that let's you simulate both putting money in - lump sum and incrementally - and also take money out. I'll see if I can find a link to a live version.