As usual, when I am trying something new, I try many simple examples.

I have two lists of 4 date columns each (+title, etc). List1 has only 1 row.
The workflow is on creating new rows in List2.

At creation of new item in List2, using SPD (MOSS) I tried:
1) copying a date from List1 -> new row of List2: WORKED FINE
2) but when I tried doing a calc, the columns of "current item" were
incorrect
3) but when I tried building "dynamic string", the columns of "cur item" were
OK

What's going on?
How do I do date arithmetic from a fixed list, into the new row being added to
another list?
What is the difference between "dynamic string" and "variable"?
How do you get last row of a list to use in arithmetic?
How would you do Max or Min of a particular date column in a particular list?
Must you always use the model 1)list field->variable, 2)calc with variable,
3)variable->list field?