You can set the scale of a Foto 3D object through the File Menu > Settings dialog > Mat Scale Settings function:
Mat Scale Settings
This setting affects the scale of the exported object. Foto 3D CX exports model in VRML in meter units or in 3DS in mm units. By entering the length of a "mat unit" the exported model will be accurately scaled.
To obtain the actual length of the mat unit, simply measure the mat unit marker printed on the physical calibration mat. This is also the radius of the thin outer circle printed around the dots - you can measure the diameter of this circle and then halve your measurement.