Duplicate triangle from first construction of Action Geometry, also documented at
I am building this using the basic tools of geometry, the compass and straightedge, then forming it into a rigid card that can be used to create more geometric constructions quickly. Many 3 dimensional future constructions are based on this tool. I make it with my logo and art and reference URL but adapt as you see fit this is all more than public domain, changes and duplication are both encouraged.
Step 1: Draw Line, Mark Off 3 Inch Segments
I'm bending the rules of classical geometry here and using 3 inches in real units for uniformity. Start with drawing a line about 7 inches long and marking off 3 inch segments with a pen and ruler.
Step 2: Draw 3" Circles With Compass
Use compass to draw 3 inch diameter circles from all marked points(there are three of these from the previous step).
Step 3: Connect the Dots
Use ruler to draw lines connecting all the vertices, making 3 triangles, each 3 inches on a side.
Step 4: Mark Half Way Points
This could be done with the ruler, marking off 1.5 inch segments, or it can be done with a classical straightedge(no markings) by connecting corners that got through midpoints of other triangles. This is one of the reasons it's helpful to draw several triangles even if you only want one.
Step 5: Cut Up the Big Triangles Into Little Triangles
Draw all the lines to cut the 3 inch triangles into 1.5 inch triangles, of which there are now 9.
Step 6: Color the Triangles In
Write whatever information you want on the triangles, ideally a URL for how to make another triangle, which could be a link to this page, Color in with big solid colors that are easy to see. I use yellow in the middle, then go around with red, blue and green, but this could be a color scheme more relevant to your interests.
Step 7: Cut Out
Cut the triangles out with a scissors. You need 2 but made 3 so keep the two best ones and put the other aside for future use.
Step 8: Trace and Cutout Triangle From Cardboard Box
I use a cereal box, which is thin but stiff cardboard. Trace the triangle from previous steps, then cut out very carefully following right down the middle of your lines.