We present CapTUI, an innovative drawing tool that detects tangible drawing instruments on a capacitive multi-touch tablet. There are three core components to the system: the tangible hardware, the recognizer used to identify the tangibles and the drawing software that works in tandem with the tangibles to provide intelligent visual drawing guides. Our recognizable tangible drawing instruments are a ruler, protractor and set square. Users employ these familiar physical instruments to construct digital ink drawings on a tablet in an intuitive and engaging manner. The visual drawing guides enhance the experience by offering the user helpful cues and functionalities to assist them to draw more accurately. A user evaluation comparing CapTUI to an application with passive tools showed that users significantly preferred CapTUI and found that the visual guides provide greater accuracy when drawing.