How can I reset this number to 0 without to have to quit the software?

[rich2005]

There are more codes available than shown in Edit -> Preferences

Code:

%f: base filename
%F: full filename
%p: PDB id
%i: instance
%t: image type
%T: drawable type
%s: user source zoom factor
%d: user destination zoom factor
%z: user zoom factor (percentage)
%D: dirty flag
%C: clean flag
%B: dirty flag (long)
%A: clean flag (long)
%m: memory used by image
%M: image size in megapixels
%l: number of layers
%L: number of layers (long)
%n: active drawable name
%P: active drawable PDB id
%W: width in real-world units
%w: width in pixels
%H: height in real-world units
%h: height in pixels
%u: unit symbol
%U: unit abbreviation
%X: drawable width in real world units
%x: drawable width in pixels
%Y: drawable height in real world units
%y: drawable height in pixels
%o: image's color profile name
%e: view offsets in pixels
%r: view rotation angle in degrees

So not difficult to make your own bespoke title or status bars - but the defaults are usually best.