Hi All,
I've implemented multi-level 'undo' for calculations and manual map editing in the latest developmental build of L3DT Standard and Professional. For those interested, there are some more notes and details in the dev weblog.
Please give it a try and let me know what you think, and please report any bugs that you find. Feedback from users is always welcome.
Cheerio,
Aaron.
PS: If you are infallible and/or want your calculations to run more quickly, you can disable 'undo' by un-checking the 'Edit->Enable undo' menu option in L3DT.