This is a lightweight modular Shot Put, Hammer, Weight Throw Circle.
 
Using keyed foam mats we cut out the proper size 2.135 meters throwing circle. We used a large laser router to cut a smooth accurate circle to the proper size. The pads lock together to form the throwing circle.  We use dumbbell weights to hold the circle down or you can use any heavy object on two or more of the segments.  The mats are heavy-duty 3/4 inch thick. The circle is accurate to within .5 diameter due to expansion and contraction of foam.  We get material in 3 different colors and depending on availability the one shipped may be sky blue, silver/grey or black.  
 
The 4-degree engravings are 0. 90.180, 270.  This makes it easy to get visual cues for footwork drills and throwing.  Our theory is that every other sport has field or court markings. Why not for throwers?   Imagine Stephen Curry playing with no floor markings to reference.  The visual cues give a better feeling and knowing how your footwork is working.