This hack is for people who is difficult to obtain grid ruled index cards.
0. What you need is only a highlighter with 5mm width. We don't need
ruler, you can measure using pen's head.
1. Slide index cards's top so that easy to line.
2. Leave one pen head width as margin.
3. Then put four lines with approximately 1 mm spacing.
That's all. You may finish in 20 seconds.
Now you can use tag with blank or ruled index cards! :)