Help!: distance window in mapping mode

On my home computer I get a little window in the lower right (in the map mode) that tells me the exact distance of the map I'm making but for some reason that little window doesn't show up on my work computer.  Any ideas why? I've looked through the site and am unable to find a place to turn that on and off.  I suspect it's something right in front of me...

Thanks for your help.

Liza