It is slightly more complicated than that. I only ask because Shapeways asks for a unit of measure. If the object was drawn at 1:1, selecting either mm, inches, or meters when uploaded to Shapeways would change the printing size considerably for the same file.
For example, if the navigation chair was drawn in decimal inches, it should measure 39.72, if it was drawn in decimal feet it would measure 3.31. While both are considered 1:1 or full scale, the decimal feet drawing is 12x smaller than the other.
A unit of measure would be important because, if it was drawn in decimal feet, the drawing would have to be scaled up by 12 to convert it to decimal inches before I scaled it down to 1/48. Likewise, if it was drawn in CM, the drawing would have to be scaled up by 10 to convert it to mm before I scaled it down. I hope this makes sense.