This is an adaptation of a design for a scale made from a postcard, paper clips, and a coin by Arvind Gupta. It can be viewed here.
You can view the finished scale in Step 7.
Step 1: Tape the CDs Together
Step 2: Prepare Finish Nails
Step 3: Drill the CDs With a Finish Nail
Step 4: Insert Axles and Begin Wire Attachments
Cut some steel wire (about #15 gage) 7 inches long. This piece will make the handle by which the scale is held. Bend and/or twist it to your liking. With a needle nose plier make a loop in each end of the wire. Try to make the loops on the same plane with each other so the axle rests in them while the axle is level. Slip the handle loops over the ends of the axles.
Step 5: Make the Wire Hanger for a Clothespin
Cut a piece of #15 gage wire 16 inches long. Bend and insert it in the clothespin as shown. It may be twisted together with about 3 twists above the ends of the clothespin handles.
Step 6: Attach the Clothespin Hanger to the Other Axle
Step 7: As It Looks Assembled
All that remains is to do the calibration.
Step 8: Calibration
I did an Internet search for the weight of a US Quarter ($0.25 piece). Those made since 1967 with the copper core weigh 5.67 grams each. I used a metric to English conversion calculator. In ounces that is 0.20003 ounce each. That means five post-1967 US Quarters weigh exactly one ounce. (No one at the Post Office will worry much about anything after four decimal places.)
A plastic Baggie for a sandwich has a negligible weight. I attached a Baggie to the clothespin and put five US Quarters into it. When the scale came to rest, I made a mark for 1 ounce at the point where the hanger wire for the clothespin crossed the frosted tape. It is the leftmost mark of the three you see. Then I added five more Quarters for 2 ounces. It is the second mark. The third mark is for fifteen Quarters or 3 ounces. You can add "1", "2", and "3" to your marks to avoid confusion later about their meaning.
The marks appear to be a bit to the side of the wire hanger/indicator, but they really are not. That is because I did not take the photo straight on to the CD. I wanted to avoid reflections that would make the photo less useful.
The more carefully you make and read your calibration marks, the more accurate your scale will be.