Normally the entire table is boxed, and gridlines start at the left boundary and enclose the entire grid. To leave the first column outside the box:

nltOffset 1

Note that it will still have the heading above – insert a null title element if you want the titles to start at column-2 also.

You can also choose to start drawing the horizontal gridlines from a given column – this is set with the second element, for example:

nltOffset 0 2

This is often useful with merged cells, as you do not want to draw the grid through these.

See also ...
nltKeyStyle – set column key style