To perform operations on a line, select it in the table and use the line toolbar.
By default, new lines are added at the end of your session table. You can change this behavior by selecting a line and using the insert mode button.
You can also insert before, after or replace the selected line.
Select the line you want to replace, enter the new expression at the rcalc prompt and hit Enter.
Use the SHIFT-Enter binding to directly replace the selected line, whatever the insert mode.
Select the line you want to move, and hit the Move up or Move down button.
While moving or removing lines, you change all lines below them. This can lead to undefined expressions (e.g., if you remove a variable that is used below).
Undefined lines are kept until you decide to remove them.