This stylish scale (if I do say so myself) can't be beat for simplicity - it's really just a lever and a rolling fulcrum. Just push it left or right on the roller until it tips, and then the roller position marks the weight. Update: I've updated the paper gauge with a slightly more accurate version. You'll need 50 pennies, two O-rings (1/8" thick by 3/4" ID), and two 6-32 x 1/4"L socket cap screws. I printed the beam, roller, tray and penny bin in PLA with 0.2mm layers, 3 perimeters, and 20% infill. You'll need supports turned on for the beam (which prints on its side), but they break away really easily. To assemble, first insert the roller by flexing the retaining strap on the bottom side of the beam so the roller will fit through. Next stretch the O-ring tires onto either side of the roller. Screw the penny bin onto one side of the beam with one of the 6-32 screws. Screw the other 6-32 screw directly into the hole on the opposite side. (The tray has an indentation in the bottom that sits on top of the screw head.) Print the paper gauge strip and attach it to the front beveled edge of the beam with double-sided tape. Finally, put 13 pennies each in two opposing penny slots and and 12 pennies each in the other two opposing penny slots. To use the scale, put what you want to weigh in the center of the tray (things placed off-center won't be weighted as accurately) and place the tray on the end of the beam. Make sure the scale is on a flat, smooth surface (like a countertop!). Push the entire scale left or right until it tips on the roller. The position of the center of the roller on the gauge strip will indicate the weight. The gauge strip is calibrated for 50 pennies. If you want a more accurate scale for lighter amounts, you can remove some of the pennies and print a new gauge strip for the opposite side of the scale. (You can use your leftover pennies to calibrate the new gauge - each penny weighs 2.5 grams.)