> I make a line. Then I make a copy. When, should I enable or disable history?
> I try to make the trapezoid but no matter what I choose (history on or off) it is always the same.

Sorry I missed this part.

To create the problem situation here is what you do.

First draw one horizontal line. Then select it and do Transform/Copy and create a copy of it either above or below. Select the new copied curve, and run Edit/History and click "Enable update".

Now history updating is turned on for the copy.

Now select the original line, use Edit / Show pts to turn on points, and then deselect everything and drag a point of the original line. Now you should see both lines update when you drag a point from the original line.

With history for the copied line turned on like this, it is now difficult to make a trapezoid shape by trying to edit the first curve to make it longer or shorter, because when you edit it the second curve also changes to match it instead of staying in place. This is what would happen if history was turned on for all operations by default.

- Michael