The sloping line

My first row of lettering drifted steadily downhill. Arun's response was succinct: he told me to place a ruled sheet beneath the page so that its dark horizontal lines showed through. The method proved effective at once. With the hidden lines as a guide, I produced a level row without leaving pencil marks on the finished work.

From the passage, select two words or phrases that describe the style and usefulness of Arun's response.