threshold of a stack

[vigny]

Hi. I’m working with gray-scale stacks. I want to threshold the whole stack to a selected value I get from the histogram (obtained including all the slices). When I apply that value the windows “Convert to mask” appears: what does the command “Calculate threshold for each image” mean? That it would apply the Isodata algorithm for each image and not the value I chose?

Thanks very much for your help.
Bye

Elisa