Technical Savvy: Resizing with a Proportional Scale

My background as a technical illustrator makes me privy to all sorts of handy tools.  This proportional scale is one that I have used for years to determine, with unfailing accuracy, the percentage required to resize an image or design.  It is so simple to use and so handy that I am surprised that few outside of the technical/drafting world seem to have discovered it.  Although I know and can use the mathematical formula to determine the resizing percentage, I much prefer the wheel.  It requires no brain power, just a simple twist of the dials.

Find the original size on the inner wheel and the reproduction size on the outer wheel.  Twist the wheels to align the two numbers and the percentage at which the design must be printed appears in the window; completely math free!