Why are interior dimensions "off" by 1 inch?

[mollybydesign]

I'm working through the Home Designer - Kitchen Design - Video | Home Designer (homedesignersoftware.com) training video and I notice that on the presenter's screen, as well as my own, interior dimensions for what looks like the same space differ by 1 inch. Why is that? Does it matter? How does the presenter know which one of these to adjust when they are adjusting the walls? 

 

Thanks for your help! 

[Rookie65]

Look at what the arrows point to. The top is from surface to surface. The lower one is framing to framing. With 1/2" drywall, the one inch difference comes from that. Read through your reference manual for seeing how you can set dimensions to measure how you need for your project.

[mollybydesign]

Thanks @Rookie65!