losing dimensions in pepakura?

This issue is happening in several models I import. I figure it is just a basic principle Im missing and was hoping someone could point me at the obvious.



Say I make a cube in sketchup 5mmx50mmx50mm. I open and unfold the cube in pepa just fine except for fact it comes out 50x50x49. I keep losing a mm on my models. What am I overlooking?