Step 5   Now that the two marks have been made, the worker takes a straight-edge, in this case a 4' level, and joins the two marks. For the straight-edge you can use a number of different items, but be very cautious of using pieces of wood--very little lumber is perfectly straight. Instead, use something like a level or one of our metal yardsticks. Of course, if your panel is wider, you may have to make more than one mark, then join those marks together. But remember, as said at the beginning, Measure Twice--Cut Once!!!