Introduction of an Undo button

For us to develop this ability we would like to understand the areas of the application that would be the highest priority for an undo function. If you have a requirement for this please add comments with the area of the system you would most like to see this feature.

I spend a large chunk of my time in the Takeoff element of the software, so the addition of an 'undo' function there would be a great help. It may only speed things up minimally, but it's the simplicity of it that appeals most. A 'one click' option would improve the user interface significantly, I feel.