In my Bav. 38 / 2003 is the old analog Calira Panel 201 for switches and Water/Battery Level Meter. Unfortunately the Water Level need calibration from time to time. Behind the instrument is a PCB with some potentiometers for calibrating various levels.
I contacted company CABOTRON Elektonik in South of Germany who took over the CALIRA products and service. The friendly people sent me a calibration instruction and the layout of the PCB with alocation of the trim poti's.
See attachments.
Here the German text with translation:
Sehr geehrter Herr Landes,
anbei die Trimmerbelegung.
Zum Einstellen einfach die Frischwassersonde aus dem Tank nehmen und die zwei längsten Stäbe überbrücken = ¼, dann immer den nächst kürzeren Stab mit dazu nehmen und jeweils an dem dafür vorgesehen Trimmer die Einstellungen vornehmen.
Mit freundlichen Grüßen
Friedrich Eickmann
saying: take out fresh water sensor from tank, conncect the two longest sticks = 1/4 full, then "add" the next shorter stick (now three are connected) = 1/2, and so on.
I hope this is clear.