This turns out to be a simple design. The only real obstacle is making sure there’s room for the numbers.
Here’s an easy way to draw the tablets:
Start by drawing a square. Try to make it large enough that you can easily split it into 9ths — make the square 9 by 9 on a grid for example.
Split the square vertically into three rectangles by outlining the middle 9th. Or to put it another way, make the rectangles 4/9ths, 1/9th, and 4/9ths.
Draw a horizontal line 2/9ths from the top.
Place marks on the top side of the square on the center of each of the larger rectangles.
Use arcs to connect those marks to the places where the horizontal line touches the rectangles.
Now that the overall design of the tablets is done, here’s how to easily position the numbers. Draw a line vertically through both tablet’s middle. These lines show where the center of the tablet is, and so you can position the numbers easier.
Now divide the rectangular potion of each tablet into 9ths. Each of the lower 8 sections will contain a different number.
There’s no right or wrong about how the numbers are arranged. Just be sure to use the lines drawn in the last two steps to guide you in adding them.