I based my original designs on the only good surviving example we have which has five courses and was made around 1450 by Hans Ott in Nuremberg (incredibly for such an early period, it has a maker’s label inside it) during a time when I would suggest that the use of gitterns was in decline. However, judging by all the earlier iconographic evidence it had changed very little in concept over perhaps the preceding two centuries, although the number of strings or courses of strings varied between 3 and 6! But were they all classed as the same instrument? We don't know. Although its shape indicates an obvious similarity to the lute it has also been suggested that the gittern was a forerunner of the guitar.
A gittern was the first instrument I ever built when I started learning luthiery and I have now made quite a considerable number of them - tweaking the designs here and there to meet the needs of individual customers - whilst travelling the learning curve.