Diagram 2: Nomogram
A Nomogram is a graphical computing aid, a paper calculator so to speak. The idea is that you can read off one missing value when the others are given.
The picture below shows various Rocket engines. The parameters are: Exhaust velocity (horizontal), rocket speed (vertical) and the proportion of fuel over rocket weight (diagonal).
For example, we'd like to travel from Eart to Venus with at most 1g acceleration. Conveniently there is a horizontal line labeled like that starting near word "destination" on the top left.
Now we're left to trade off exhaust velocity against mass ratio. If we only want to take an additional 50% fuel with us (compared to the unfueled rocket weight) we'd need to have an exhaust velocity around a million meters per second.
You need a fusion engine to do this and the problem is: We have none today and i can't see we will in the near future. So we'd probably be better off taking a slower route.
I'd like to remark that this Nomogram would have done wonders to the realism of so many sci-fi stories...
Other, maybe graphically more interesting ones, relate multiple paramters utilizing skew or warped coordinate systems. Wikipedia has a wonderfully warped and skewed diagram on it's nomogram page: