If working in an orchestral situation, choose the A reference (440, 441, etc.) Type in current fundamental frequency as exact Hz or as Note name, choose current partial. This device will display it's frequency and nearest note name with cent deviation (in blue) and play it if you push "start". To modulate, choose a new partial on the "Modulate to Partial" line. It will calculate a new fundamental from which to base a new harmonic series. This will be displayed in the "Modulated Preview" areas as a frequency in Hz and a note name with cent deviation (displayed in grey). Once you hit "Make Current", it will update the current fundamental frequency, current note, and current partial. Note that the output dislpay of the current partial frequency in Hz and current nearest note (in blue) will NOT change - nor will the pitch if you have pushed "Start" for playback. The only thing that will have changed is the current fundamental. Now when you choose a different current partial, the partial will be from that new series.