This bookmark was made from plastic file folders of contrasting colors. Make the size according to that of a typical book. The red piece should be a bit longer than the book is high. The blue piece should be a half of an inch wider than the red piece. If you wish, you may round the corners, especially on the red piece.
Step 1: Cut the Long Piece
Step 2: The Slider
I have a hole punch that makes 1/8 inch holes. Make one hole near the top of the slider. Make two holes near the center of the slider.
Step 3: Mark the Slider
Step 4: Cut the Slots
Step 5: Join the Slider to the Long Piece
Step 6: Both Sides Now
Step 7: Cut a Notch in the Slider
Step 8: How to Use
When a book is open the page on one side will have an odd number. The page on the other side will have an even number. If you are stopping on a page with an odd number, turn the bookmark over so one hole in the slider will be visible as you open the book from the front cover. One is an odd number. Turn the side with two holes up if you are stopping on an evenly numbered page. Two is an even number. (The page number in the yellow box is 185. The yellow arrow points to one hole in the blue slider.)
Move the slider down to the line where you want to begin again. See the yellow underline. (I have gotten into the habit of aligning the bottom of the page with the end of the long piece of the bookmark, and letting any extra length protrude from the top of the page. If the bookmark moves up or down in the book, I just pull the bottom of the bookmark in line with the bottom of the page and the line indicator is back where I had placed it.)
Open the book from the front cover and you will know immediately on which page and which line you are to begin reading again.