Ruler measurement does not give the result that I expect

Hello, I have been using slicer and am comfortable with a few of the modules. When I use the measuring tool (ruler) point to point, on an area that know would be approximately 1mm in length, it shows a number of :55.5? I have the ruler set to measure at mm increments. What am I doing wrong?

Hi -

What kind of data are you measuring? If it’s from something like a jpg or tiff file, then you need to set the pixel spacing so that the measurement tools are calibrated. You can do this in the Volumes module.

It’s an nrrd file. Thanks. I’ll check the volumes module.