When writing notes and underlining in wide margin Bibles, I prefer to use a ruler to keep the lines straight. Of course, a ruler is difficult to use when the page isn’t completely flat. Business cards or index cards help, but they’re thin and if they’re made of paper they can soak up the ink and smear it back onto the page. They don’t last long because the ink damages the edges. They’re cheap and they’re usually easy to find, but you do need a lot of them.
My favorite way to underline is to use a 6″ flexible ruler, from GT Luscombe. It’s made specifically for Bible marking. It conforms to the bend of the page, making it easy to use even if the page isn’t completely flat. You can bend it and it straightens back out on its own. It’s clear, so you can see how you’re placing the lines on the page. It’s made of plastic, so it doesn’t soak up the ink. It costs less than a dollar.
It has a ruler in inches on one edge and a scalloped pattern on the other edge to create some interesting lines. It also includes the names of the books of the Bible under the type of writings they are. GT Luscombe also has a non-flexible ruler with the books of the Bible if you prefer.
The scalloped pattern is great for creating designs that stand out. The straight edge makes it easy to draw clean lines, and it can be used in the margins to create an invisible line to write on. Since the ruler is clear you can see how close your lines are to each other. You can tell in the image above which lines are drawn by hand and which use a ruler. The ruler is a lot cleaner.
You can get the Flex Ruler from Christianbook and many Christian bookstores.
Video With Demonstration
This video includes a demonstration of the Flex Ruler: