If your desk isn't cluttered, you aren't doing your job. Gadget-building geeks know this adage well, thanks to resistors. The tiny components police electricity's flow, yet it can take dozens of kinds to perfect a circuit (such as to spin a motor at a precise speed). Electronics hobbyist George Graves knew devices called decade boxes allowed users to dial in different levels of resistance, but retail models seemed expensive and confusing. So Graves built his own with used parts. Now you can too.