Hello,

When I set sigma a to 0.1mm and sigma b to 1mm, the sigma h values for each measurement are between 0.2 and 0.4, while when I set sigma a to 1mm and sigma b also to 1mm, I get sigma h values between 0.8 and 0.9.
Whats is correct?

Your question cannot be answered in this way. It depends on your assumption and experience.
How do you evaluate the value for σb? The value may be specified by the manufacturer of the instrument, but this does not mean that you have reached this value.

Have a nice weekend
Micha