Making Circles

• 1). Count the number of columns in your table of data. For example, a table to convert temperature readings from Fahrenheit to Celsius would have just two columns.
  
  
• 2). Use a compass to draw circles onto the cards. You will need to make as many circles of card paper as there are columns in your table. It helps to draw each circle on a piece of card of a different color. Make your first circle around 10 inches across. Make the next circle smaller, say, 9 inches. Make each subsequent circle smaller again.
  
  
• 3). Count the number of rows in your table of data that you wish to use. For example, you might decide to use 12 key conversions from a longer set of Fahrenheit-to-Celsius information.
  
  
• 4). Divide the number 360 by the number of rows of information you wish to use. You may find a calculator helpful for this task. Your answer will give you the angle of a single segment, or "piece of pie" on your chart. For example, 360 divided by 12 rows gives the answer 30. Each piece of the pie would have an angle of 30 degrees.
  
  
• 5). Use a protractor to mark off the largest cardboard circle into equal segments, or "pieces of pie." To do this, place the center of the protractor on the center point of the circle. Look for the number you calculated---in our example 30 degrees---on the outer edge of the protractor. Make a mark on the cardboard next to this number. Rotate the protractor, keeping it centered, until the "zero" on the outer edge lines up with your pencil mark. Now mark the new position of the number you calculated, in our example 30 degrees. Keep rotating and marking, until you have turned the protractor through one full circle.
  
  
• 6). Draw lines with a ruler and pencil to link each of your marks to the center of the cardboard circle. You should end up with the circle divided into equal wedge shapes, like the segments of a pie. Now draw pie segments on each of your smaller circles in exactly the same way. Use scissors to cut a small square hole in just one segment of pie in each smaller circle. Leave your biggest circle whole.
  
  

Assembling the Chart

• 1). Pile one circle on the center of the next, starting with the largest and ending with the smallest.
  
  
• 2). Push a brass paper fastener through the center of all the cardboard circles.
  
  
• 3). Open the legs of the brass fastener on the back of the largest circle, to fix all the disks together.
  
  

Loading Information

• 1). Write the figures you wish to use from the first column of your data table, around the rim of the biggest circle. You should have space to write one figure in each "segment of the pie."
  
  
• 2). Turn your second circle like a wheel, until its square hole lines up with a figure on the rim of the chart. Into this hole write the corresponding figure from the second column of your table of data. For example, in a Fahrenheit-to-Celsius chart, if the square hole was lined up with the entry 1 F on the rim, you would write -17.2 C into the square hole.
  
  
• 3). Continue lining up the hole in your "wheel" with an entry on the rim, and writing in the corresponding figure. Keep going until you have added all the entries for the second column in your table of data.
  
  
• 4). Line up the square holes of any smaller "wheels" as described above, to enter data from any further columns of your table. When all the entries have been made, lining up all the square holes in the same "pie segment" will reveal all the entries in one complete row of your table.
  
  
• 5). To use the wheel pie chart, simply line up two or more "wheels" to compare and read off the data.