The Pigini Convertor 37/B3 is a compact free bass convertor accordion. With a 37 note right hand range with 3 voices this gives you a very flexible range. This example has 2 8' and 1 16' reeds and so it is great for traditional repertoire.
The left hand features a 78 bass stradella keyboard from D flat to C sharp. When converted to free bass you have a range of 37 notes, from C to C.
It is a C system in both hands, the free bass left hand has the lowest notes towards the sky.
This instrument is second hand, with some cosmetic marks but it has recently been given a full service.