Hi wolfi,
Here is what IFound:
One shortcoming of the FITS standard is that the 16-bit number format is signed, producing a range of -32768 to +32767. The range of data from many cameras is 0 to 65535. To overcome this problem, MaxIm DL subtracts 32768 from each pixel prior to saving. The FITS standard requires that the BZERO and BSCALE keywords be used when the value in the array is not the physical value; MaxIm DL sets BZERO to 32768 and BSCALE to 1. Other applications that interpret these keywords correctly should automatically add 32768 to the image pixels, resulting in a correct image display. This default behavior can be overridden using the File menu Settings command.

But I agree, with bzero = offset and bscale =inverse gain you could even produce fits files containing the number of electrons per pixel....

Regards

Dirk

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