Shigeru Ban has designed a retractable, refillable "SCALE" pen for ACME Studio that was inspired by the architect's ruler. The aluminum pen, designed to fit comfortably into your hand, serves as a fully functional architect's scale outfitted with a ballpoint pen that retracts with a simple twist of the pen's two halves.
As Design Milk specifies, SCALE is compatible with ACME’s P900 and easyFLOW ballpoint refills. You can purchase your own for $90.