An algorithmic combo-instrument slide ruler comprising one common part working in cooperation with two interchangeable parts selected from separate multitudes of unique yet related parts. An opaque slidable combo-instrument tuning card is selected having thereon information resembling a stringed instrument, having fingering positions represented in equivalent keyboard keys laid out in a multi-tier octave isolating manner. A semi-opaque rectangular sleeve housing comprising of parent and dependant child windows arranged in a reticulated manner, working within stationary alignment with a selected semi-opaque scale or mode insert comprising of a scale or mode relevant predetermined array of finger position windows and dependant finger position data boxes, allows for a visible and semi-visible view of the combo-instrument card there through, showing available fingering positions through parent windows and music reference information through relevant child windows. By sliding combo-instrument card, music reference information pertaining to the selected scale or mode insert can be obtained in every key in selected tuning.