The DG Charango Chord Patterns Android application is very easy to use.
The screen is divided into 4 regions, as shown in the following figure:
There are four regions: 3 button grids, and one central graphics frame:
When you are operating the application, all you have to do is to choose one button from each of these button grids.
Immediately after, the chosen chord pattern is displayed on the central frame, the yellow area on the figure shown above.
The central frame displays the chosen Charango chord pattern graphically, and also by name (on the right).
The graphical image displays only five frets at a time, which is sufficient to display all fingering positions of any chord.
When the chord pattern is close to the head, or nut of the instrument, it shows a double vertical line.
When the chord pattern is on higher frets, it shows a number on top of the first fret, as in the figure above; all subsequent fret and number positions are relative to this fret number. This is the standard way of representing Charango chord patterns.
When you tap on the fretboard, it switches between displaying the notes of the chord pattern, or the intervals.
The intervals are particularly important, because, when you are playing solo notes, you might want to land on chord notes on a beat.
Pressing the 1, 5, or 9 buttons will take you straight to the pattern as seen on those frets, respectively;
alternatively, press the ">>" or "<<" buttons to see the pattern starting from different frets (such as 2, 3, 4, 6, 7, etc).
The strings are positioned from the viewpoint of a Charango player, with the instrument on its lap, (head on the left, body on the right) looking down at the fretboard, with first string course on top of the image (bottom of the Charango, further away from you), and fifth string course at the bottom of the image (top of the instrument, closer to you). Other books and charts represent the chords in different orientation, but we find this way very intuitive.
On the left of the nut, white circles represent the strings that can be played open ("o") on that particular chord pattern.
On the example shown above, there is an "o" on the 1st, 2nd, and 3rd string courses, because they are part of an A major chord.
The circles in pink color represent the possible finger positions, showing the notes (or intervals) of the chord pattern, as they are placed on the fretboard.
A key point to remember is that this application is not intended to show you chords, but to help you deduce them.