Hans Palm's Accordion Page: Registers

ABOUT REGISTERS

The registers or stops used in both the left and right hand sides could be marked using either similar sounding instrument names or using dot markings and organ terminology. A combination of instrument names and dot markings is also common.
There's no single standard for naming the stops using instrument names. It's recommendable to use dot markings in sheet music and in order to communicate the correct setting to an ensemble.
The maximum number of reeds that are used simultaneously when pressing a single key on the treble side, determines the maximum number of stops. The same applies to the bass stops when producing a single bass note or a note used to construct a chord.
The theoretical maximum number of registers or stops is 2^N-1, where N is the maximum number of reeds used simultaneously for a note. The -1 covers the case when no reed is sounding at all - a meaningless combination. Examples:

N = 3 or 4 is most common and I've never seen an accordion with N > 5.
In practice the number of stops is usually reduced from the theoretical maximum. This is done in order to reduce weight. Too many stops could also be confusing and some of them would sound very similar to each other. Most players use a few favourite stops only.

The most common dot markings are built upon combinations of the following basic elements:

4 ft - The length of an organ pipe sounding one octave above the notated value

8 ft - The length of an organ pipe sounding at the notated value

16 ft - The length of an organ pipe sounding one octave below the notated value

The 8 ft may have two or even three different reeds, tuned slightly apart. Used together, the famous musette sound is produced. Depending on the tuning distance, the tone is "wet or dry" . Possible dot markings:

or or or